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/repo/issue/view_content/pull.tmpl

@@ -340,7 +340,6 @@
 						{{end}}
 						<div class="ui divider"></div>
 						<script>
-							<!-- /* eslint-disable */ -->
 							(() => {
 								const defaultMergeTitle = {{.DefaultMergeMessage}};
 								const defaultSquashMergeTitle = {{.DefaultSquashMergeMessage}};