Fix eslint parsing errors, remove eslint-plugin-html (#20323)

Introduce a separate .eslintrc in the Vue components folder to
selectively enable vue-eslint-parser there, so that the rest of the
files can use eslint's core parser which can deal with hashbangs.

The fact that the eslint-disable comments worked in HTML was a
unintended side-effect of the files being parsed via vue-eslint-parser,
so I had to disable the parsing of these files in .eslintrc.yaml to make
it work, and finally decided to remove eslint-plugin-html as it causes
more issues than it solves.

templates/base/head_script.tmpl

@@ -4,7 +4,6 @@ If you are customizing Gitea, please do not change this file.
 If you introduce mistakes in it, Gitea JavaScript code wouldn't run correctly.
 */}}
 <script>
-	<!-- /* eslint-disable */ -->
 	window.addEventListener('error', function(e) {window._globalHandlerErrors=window._globalHandlerErrors||[]; window._globalHandlerErrors.push(e);});
 	window.config = {
 		appVer: '{{AppVer}}',