Improve template system and panic recovery (#24461)

Partially for #24457

Major changes:

1. The old `signedUserNameStringPointerKey` is quite hacky, use
`ctx.Data[SignedUser]` instead
2. Move duplicate code from `Contexter` to `CommonTemplateContextData`
3. Remove incorrect copying&pasting code `ctx.Data["Err_Password"] =
true` in API handlers
4. Use one unique `RenderPanicErrorPage` for panic error page rendering
5. Move `stripSlashesMiddleware` to be the first middleware
6. Install global panic recovery handler, it works for both `install`
and `web`
7. Make `500.tmpl` only depend minimal template functions/variables,
avoid triggering new panics

Screenshot:

<details>

![image](https://user-images.githubusercontent.com/2114189/235444895-cecbabb8-e7dc-4360-a31c-b982d11946a7.png)

</details>

1 files changed, 0 insertions, 11 deletions

diff --git a/web_src/js/bootstrap.js b/web_src/js/bootstrap.js
index 4f88c600f5..f0b020ce1c 100644
--- a/web_src/js/bootstrap.js
+++ b/web_src/js/bootstrap.js
@@ -20,10 +20,6 @@ export function showGlobalErrorMessage(msg) {
  * @param {ErrorEvent} e
  */
 function processWindowErrorEvent(e) {
-  if (window.config.initCount > 1) {
-    // the page content has been loaded many times, the HTML/JS are totally broken, don't need to show error message
-    return;
-  }
   if (!e.error && e.lineno === 0 && e.colno === 0 && e.filename === '' && window.navigator.userAgent.includes('FxiOS/')) {
     // At the moment, Firefox (iOS) (10x) has an engine bug. See https://github.com/go-gitea/gitea/issues/20240
     // If a script inserts a newly created (and content changed) element into DOM, there will be a nonsense error event reporting: Script error: line 0, col 0.
@@ -37,13 +33,6 @@ function initGlobalErrorHandler() {
   if (!window.config) {
     showGlobalErrorMessage(`Gitea JavaScript code couldn't run correctly, please check your custom templates`);
   }
-  if (window.config.initCount > 1) {
-    // when a sub-templates triggers an 500 error, its parent template has been partially rendered,
-    // then the 500 page will be rendered after that partially rendered page, which will cause the initCount > 1
-    // in this case, the page is totally broken, so do not do any further error handling
-    console.error('initGlobalErrorHandler: Gitea global config system has already been initialized, there must be something else wrong');
-    return;
-  }
   // we added an event handler for window error at the very beginning of <script> of page head
   // the handler calls `_globalHandlerErrors.push` (array method) to record all errors occur before this init
   // then in this init, we can collect all error events and show them