Move `public/*` to `public/assets/*`

Some old PRs (like #15219) introduced inconsistent directory system.

For example: why the local directory "public" is accessed by
`http://site/assets`? How to serve the ".well-known" files properly in
the public directory?

For convention rules, the "public" directory is widely used for the
website's root directory. It shouldn't be an exception for Gitea.

So, this PR makes the things consistent:

* `http://site/assets/foo` means `{CustomPath}/public/assets/foo`.
* `{CustomPath}/public/.well-known` and `{CustomPath}/public/robots.txt`
can be used in the future.

This PR is also a prerequisite for a clear solution for:
* #21942
* #25892 
* discourse.gitea.io: [.well-known path serving custom files behind
proxy?](https://discourse.gitea.io/t/well-known-path-serving-custom-files-behind-proxy/5445/1)

This PR is breaking for users who have custom "public" files (CSS/JS).
After getting approvals, I will update the documents.

----

## ⚠️ BREAKING ⚠️

If you have files in your "custom/public/" folder, please move them to
"custom/public/assets/".

---------

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Giteabot <teabot@gitea.io>

- Update all JS dependencies to latest version
- Enable unicorn/prefer-node-protocol and autofix issues
- Regenerate SVGs
- Add some comments to eslint rules
- Tested build, Mermaid and Katex rendering

- Remove __dirname, use file URLs instead
- Upgrade fabric dependency
- Use fs/promises syntax, this breaks node 12 but we require 14 already

The change in public/img/favicon.svg is not caused by the fabric
upgrade, but it seems it was not properly generated when introduced.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

* Changed the filename of the favicon SVG

This allows the user to have a favicon which differs from the logo.

* Added favicon.svg

This is needed to accommodate the changes for allowing the user to have a differing logo and favicon

* Adjusted page to accommodate what icon is used as favicon

* Added functionality to also generate the favicon.svg via generate-images.js

* Adjusted the description for the new favicon compatibility

Co-authored-by: silverwind <me@silverwind.io>

* Updated generate-images.js to generate favicons from a separate favicons.svg file

This belongs to PR #18542.

* Added description on how custom favicons can be generated

* Replaced space indents with tabs

* Synced changes with current state of the file

* Synced changes with current state of the file

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

- Update all JS dependencies to latest versions
- Add new lint rules, enable es2022 eslint parser features
- Disable github/no-then, I feel the rule was too restricting

* Add new JS linter rules

Adds a few useful rules from eslint-plugin-github. Notable changes:

- Forbid dataset usage, its camel-casing behaviour makes it hard to
  grep for attributes.
- Forbid .then() and .catch(), we should generally prefer await for new
  code. For rare cases where they are useful, a eslint-disable-line
  directive can be set.
- Add docs js to linting

* also enable github/array-foreach

* small tweak

Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

* Make build scripts compatible with node 12

"fs/promises" is not in node 12, use a more compatible way to import it.
Also, lock major down versions of the image build dependencies to
prevent future surprises.

* add node_modules dependency

- Add basic frontend unit testing infrastructure using jest in ESM mode
- Rename 'make test' to 'make test-backend'
- Introduce 'make test-frontend' and 'make test' that runs both
- Bump Node.js requirement to v12. v10 will be EOL in less than a month.
- Convert all build-related JS files to ESM.

I opted to run frontend tests run as part of the compliance pipeline because
they complete fast and are not platform-specific like the golang tests.

* Update JS dependencies

- Update all JS dependencies
- For octicons, rename trashcan to trash
- For svgo, migrate to v2 api, output seems to have slightly changed but icons look the same
- For stylelint, update config, fix custom property duplicates
- For monaco, drop legacy Edge support
- For eslint, enable new rules, fix new issues
- For less-loader, remove deprecated import syntax

* update svgo usage in generate-images and rebuild logo.svg with it

* Consolidate Logos and update README header

- Remove unused `logo-lg.png`, `logo-sm.png` and `logo-192.png`.
- Consolidate `favicon.svg` and `logo.svg` to just `logo.svg`.
- Remove Safari Mask icon, it seems to work fine with just `favicon.png` (no SVG support).
- Remove Fluid Icon. It only served Firefox and SVG works just fine there.
- Update customization instructions.
- Update README.md to use SVG icon, increase logo size and center it and badges.

* Update README_ZH.md

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

* Update README_ZH.md

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

* gitea png to logo.svg

* gitea safari svg to logo

* minify svgs

* Update english docs

* Update missing section on customizing logo

* Clean up SVG

* update per feedback

* fix css style

* Delete gitea.png

* no new line at end of file

* fix newline?

Co-authored-by: 6543 <6543@obermui.de>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

* Rework 'make generate-images'

- Remove external dependencies and replace it with a node script that
  does does the same.
- Move detail removal from gitea-sm.png to favicon.png
- Remove favicon.ico and its generation, it is unused and we already serve
  favicon.png in its place.

Fixes: https://github.com/go-gitea/gitea/issues/12314

* use proper centering value for preserveAspectRatio

* fix lint

* use fabric

* better linting fix

* fix typo

* mention detail-remove class in docs