Introduce customized HTML elements, fix incorrect AppUrl usages in templates (#22861)

This PR follows:
* #21986
* #22831

This PR also introduce customized HTML elements, which would also help
problems like:
* #17760
* #21429
* #21440

With customized HTML elements, there won't be any load-search-replace
operations, and it can avoid page flicking (which @silverwind cares a
lot).

Browser support:
https://developer.mozilla.org/en-US/docs/Web/API/Window/customElements

# FAQ

## Why the component has the prefix?

As usual, I would strongly suggest to add prefixes for our own/private
names. The dedicated prefix will avoid conflicts in the future, and it
makes it easier to introduce various 3rd components, like GitHub's
`relative-time` component. If there is no prefix, it's impossible to
introduce another public component with the same name in the future.

## Why the `custcomp.js` is loaded before HTML body? The `index.js` is
after HTML body.

Customized components must be registered before the content loading.
Otherwise there would be still some flicking.

`custcomp.js` should have its own dependencies and should be very light,
so it won't affect the page loading time too much.

## Why use `data-url` attribute but not use the `textContent`?

According to the standard, the `connectedCallback` occurs on the
tag-opening moment. The element's children are not ready yet.

## Why not use `{{.GuessCurrentOrigin $.ctx ...}}` to let backend decide
the absolute URL?

It's difficult for backend to guess the correct protocol(scheme)
correctly with zero configuration. Generating the absolute URL from
frontend can guarantee that the URL is 100% correct -- since the user is
visiting it.

# Screenshot

<details>

![image](https://user-images.githubusercontent.com/2114189/218256757-a267c8ba-3108-4755-9ae5-329f1b08f615.png)

</details>

14 files changed, 24 insertions, 21 deletions

diff --git a/templates/package/content/cargo.tmpl b/templates/package/content/cargo.tmpl
index 54c40a5b0d..f78647ca69 100644
--- a/templates/package/content/cargo.tmpl
+++ b/templates/package/content/cargo.tmpl
@@ -8,7 +8,7 @@
 default = "gitea"
 
 [registries.gitea]
-index = "{{AppUrl}}{{.PackageDescriptor.Owner.Name}}/_cargo-index.git"
+index = "<gitea-origin-url data-url="{{AppSubUrl}}/{{.PackageDescriptor.Owner.Name}}/_cargo-index.git"></gitea-origin-url>"
 
 [net]
 git-fetch-with-cli = true</code></pre></div>
diff --git a/templates/package/content/chef.tmpl b/templates/package/content/chef.tmpl
index f0f8de7bd5..edc175f9be 100644
--- a/templates/package/content/chef.tmpl
+++ b/templates/package/content/chef.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-code"}} {{.locale.Tr "packages.chef.registry" | Safe}}</label>
-				<div class="markup"><pre class="code-block"><code>knife[:supermarket_site] = '{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/chef'</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>knife[:supermarket_site] = '<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/chef"></gitea-origin-url>'</code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.chef.install"}}</label>
diff --git a/templates/package/content/composer.tmpl b/templates/package/content/composer.tmpl
index 8cc18f8ba8..9acf20955c 100644
--- a/templates/package/content/composer.tmpl
+++ b/templates/package/content/composer.tmpl
@@ -7,7 +7,7 @@
 				<div class="markup"><pre class="code-block"><code>{
 	"repositories": [{
 			"type": "composer",
-			"url": "{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/composer"
+			"url": "<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/composer"></gitea-origin-url>"
 		}
 	]
 }</code></pre></div>
diff --git a/templates/package/content/conan.tmpl b/templates/package/content/conan.tmpl
index c496cee55c..138890f334 100644
--- a/templates/package/content/conan.tmpl
+++ b/templates/package/content/conan.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.conan.registry"}}</label>
-				<div class="markup"><pre class="code-block"><code>conan remote add gitea {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/conan</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>conan remote add gitea <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/conan"></gitea-origin-url></code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.conan.install"}}</label>
diff --git a/templates/package/content/conda.tmpl b/templates/package/content/conda.tmpl
index ecc26bce98..3c79d3902f 100644
--- a/templates/package/content/conda.tmpl
+++ b/templates/package/content/conda.tmpl
@@ -4,11 +4,11 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-code"}} {{.locale.Tr "packages.conda.registry" | Safe}}</label>
-				<div class="markup"><pre class="code-block"><code>channel_alias: {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/conda
+				<div class="markup"><pre class="code-block"><code>channel_alias: <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/conda"></gitea-origin-url>
 channels:
-&#32;&#32;- {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/conda
+&#32;&#32;- <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/conda"></gitea-origin-url>
 default_channels:
-&#32;&#32;- {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/conda</code></pre></div>
+&#32;&#32;- <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/conda"></gitea-origin-url></code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.conda.install"}}</label>
diff --git a/templates/package/content/generic.tmpl b/templates/package/content/generic.tmpl
index 2948d9eb02..eae4d670f9 100644
--- a/templates/package/content/generic.tmpl
+++ b/templates/package/content/generic.tmpl
@@ -4,8 +4,11 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.generic.download"}}</label>
-				<div class="markup"><pre class="code-block"><code>{{range .PackageDescriptor.Files}}curl {{AppUrl}}api/packages/{{$.PackageDescriptor.Owner.Name}}/generic/{{$.PackageDescriptor.Package.Name}}/{{$.PackageDescriptor.Version.Version}}/{{.File.Name}}
-{{end}}</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>
+					{{- range .PackageDescriptor.Files -}}
+curl <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{$.PackageDescriptor.Owner.Name}}/generic/{{$.PackageDescriptor.Package.Name}}/{{$.PackageDescriptor.Version.Version}}/{{.File.Name}}"></gitea-origin-url><br>
+					{{- end -}}
+				</code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{.locale.Tr "packages.generic.documentation" | Safe}}</label>
diff --git a/templates/package/content/helm.tmpl b/templates/package/content/helm.tmpl
index 59cdc157b4..fc190e0e45 100644
--- a/templates/package/content/helm.tmpl
+++ b/templates/package/content/helm.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.helm.registry"}}</label>
-				<div class="markup"><pre class="code-block"><code>helm repo add gitea {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/helm
+				<div class="markup"><pre class="code-block"><code>helm repo add gitea <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/helm"></gitea-origin-url>
 helm repo update</code></pre></div>
 			</div>
 			<div class="field">
diff --git a/templates/package/content/maven.tmpl b/templates/package/content/maven.tmpl
index 0b5612151c..ff89145fd0 100644
--- a/templates/package/content/maven.tmpl
+++ b/templates/package/content/maven.tmpl
@@ -7,19 +7,19 @@
 				<div class="markup"><pre class="code-block"><code>&lt;repositories&gt;
 	&lt;repository&gt;
 		&lt;id&gt;gitea&lt;/id&gt;
-		&lt;url&gt;{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/maven&lt;/url&gt;
+			&lt;url&gt;<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/maven"></gitea-origin-url>&lt;/url&gt;
 	&lt;/repository&gt;
 &lt;/repositories&gt;
 
 &lt;distributionManagement&gt;
 	&lt;repository&gt;
 		&lt;id&gt;gitea&lt;/id&gt;
-		&lt;url&gt;{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/maven&lt;/url&gt;
+		&lt;url&gt;<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/maven"></gitea-origin-url>&lt;/url&gt;
 	&lt;/repository&gt;
 
 	&lt;snapshotRepository&gt;
 		&lt;id&gt;gitea&lt;/id&gt;
-		&lt;url&gt;{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/maven&lt;/url&gt;
+		&lt;url&gt;<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/maven"></gitea-origin-url>&lt;/url&gt;
 	&lt;/snapshotRepository&gt;
 &lt;/distributionManagement&gt;</code></pre></div>
 			</div>
@@ -37,7 +37,7 @@
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.maven.download"}}</label>
-				<div class="markup"><pre class="code-block"><code>mvn dependency:get -DremoteRepositories={{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/maven -Dartifact={{.PackageDescriptor.Metadata.GroupID}}:{{.PackageDescriptor.Metadata.ArtifactID}}:{{.PackageDescriptor.Version.Version}}</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>mvn dependency:get -DremoteRepositories=<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/maven"></gitea-origin-url> -Dartifact={{.PackageDescriptor.Metadata.GroupID}}:{{.PackageDescriptor.Metadata.ArtifactID}}:{{.PackageDescriptor.Version.Version}}</code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{.locale.Tr "packages.maven.documentation" | Safe}}</label>
diff --git a/templates/package/content/npm.tmpl b/templates/package/content/npm.tmpl
index 33d51d4dfd..ea514c5263 100644
--- a/templates/package/content/npm.tmpl
+++ b/templates/package/content/npm.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-code"}} {{.locale.Tr "packages.npm.registry" | Safe}}</label>
-				<div class="markup"><pre class="code-block"><code>{{if .PackageDescriptor.Metadata.Scope}}{{.PackageDescriptor.Metadata.Scope}}:{{end}}registry={{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/npm/</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>{{if .PackageDescriptor.Metadata.Scope}}{{.PackageDescriptor.Metadata.Scope}}:{{end}}registry=<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/npm/"></gitea-origin-url></code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.npm.install"}}</label>
diff --git a/templates/package/content/nuget.tmpl b/templates/package/content/nuget.tmpl
index 4ea41fa826..8ed2f04e4a 100644
--- a/templates/package/content/nuget.tmpl
+++ b/templates/package/content/nuget.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.nuget.registry"}}</label>
-				<div class="markup"><pre class="code-block"><code>dotnet nuget add source --name Gitea --username your_username --password your_token {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/nuget/index.json</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>dotnet nuget add source --name Gitea --username your_username --password your_token <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/nuget/index.json"></gitea-origin-url></code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.nuget.install"}}</label>
diff --git a/templates/package/content/pub.tmpl b/templates/package/content/pub.tmpl
index 999e48ce82..e81439d4da 100644
--- a/templates/package/content/pub.tmpl
+++ b/templates/package/content/pub.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.pub.install"}}</label>
-				<div class="markup"><pre class="code-block"><code>dart pub add {{.PackageDescriptor.Package.Name}}:{{.PackageDescriptor.Version.Version}} --hosted-url={{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/pub/</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>dart pub add {{.PackageDescriptor.Package.Name}}:{{.PackageDescriptor.Version.Version}} --hosted-url=<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/pub/"></gitea-origin-url></code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{.locale.Tr "packages.pub.documentation" | Safe}}</label>
diff --git a/templates/package/content/pypi.tmpl b/templates/package/content/pypi.tmpl
index 1ae243813d..830ba9bd67 100644
--- a/templates/package/content/pypi.tmpl
+++ b/templates/package/content/pypi.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.pypi.install"}}</label>
-				<div class="markup"><pre class="code-block"><code>pip install --index-url {{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/pypi/simple {{.PackageDescriptor.Package.Name}}</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>pip install --index-url <gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/pypi/simple {{.PackageDescriptor.Package.Name}}"></gitea-origin-url></code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{.locale.Tr "packages.pypi.documentation" | Safe}}</label>
diff --git a/templates/package/content/rubygems.tmpl b/templates/package/content/rubygems.tmpl
index 0cb7b670b1..d8190ba4f5 100644
--- a/templates/package/content/rubygems.tmpl
+++ b/templates/package/content/rubygems.tmpl
@@ -4,11 +4,11 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.rubygems.install" | Safe}}:</label>
-				<div class="markup"><pre class="code-block"><code>gem install {{.PackageDescriptor.Package.Name}} --version &quot;{{.PackageDescriptor.Version.Version}}&quot; --source &quot;{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/rubygems&quot;</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>gem install {{.PackageDescriptor.Package.Name}} --version &quot;{{.PackageDescriptor.Version.Version}}&quot; --source &quot;<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/rubygems"></gitea-origin-url>&quot;</code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{svg "octicon-code"}} {{.locale.Tr "packages.rubygems.install2"}}:</label>
-				<div class="markup"><pre class="code-block"><code>source "{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/rubygems" do
+				<div class="markup"><pre class="code-block"><code>source "<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/rubygems"></gitea-origin-url>" do
 	gem "{{.PackageDescriptor.Package.Name}}", "{{.PackageDescriptor.Version.Version}}"
 end</code></pre></div>
 			</div>
diff --git a/templates/package/content/vagrant.tmpl b/templates/package/content/vagrant.tmpl
index 7bd686e6ab..a6a92f5ecd 100644
--- a/templates/package/content/vagrant.tmpl
+++ b/templates/package/content/vagrant.tmpl
@@ -4,7 +4,7 @@
 		<div class="ui form">
 			<div class="field">
 				<label>{{svg "octicon-terminal"}} {{.locale.Tr "packages.vagrant.install"}}</label>
-				<div class="markup"><pre class="code-block"><code>vagrant box add --box-version {{.PackageDescriptor.Version.Version}} "{{AppUrl}}api/packages/{{.PackageDescriptor.Owner.Name}}/vagrant/{{.PackageDescriptor.Package.Name}}"</code></pre></div>
+				<div class="markup"><pre class="code-block"><code>vagrant box add --box-version {{.PackageDescriptor.Version.Version}} "<gitea-origin-url data-url="{{AppSubUrl}}/api/packages/{{.PackageDescriptor.Owner.Name}}/vagrant/{{.PackageDescriptor.Package.Name}}"></gitea-origin-url>"</code></pre></div>
 			</div>
 			<div class="field">
 				<label>{{.locale.Tr "packages.vagrant.documentation" | Safe}}</label>