Fix aria.js bugs: incorrect role element problem, mobile focus problem, tippy problem (#23450)

This PR is extracted from #23346 to address some unclear (I don't
understand) code-belonging concerns.

This PR needs to be backported, otherwise the `aria.js` is too buggy in
some cases. Since there would be two minor conflicts, I will do the
backport manually.

Before: the `aria.js` is still buggy in some cases.

After: tested with AppleVoice, Android TalkBack

* Fix incorrect dropdown init code
* Fix incorrect role element (the menu role should be on the `$menu`
element, but not on the `$focusable`)
* Fix the focus-show-click-hide problem on mobile. Now the language menu
works as expected
* Fix incorrect dropdown template function setting
* Clarify the logic in aria.js
* Hide item's tippy after menu gets hidden
* Fix incorrect tippy `setProps` after `destroy`
* Fix UI lag problem when page gets redirected during menu hiding
animation with screen reader
* Improve comments
* Implement the layout proposed by #19861

<details>


d74a7efb60/web_src/js/features/aria.md (L38-L47)

</details>

templates/base/footer_content.tmpl

@@ -21,7 +21,7 @@
 			{{end}}
 			<div class="ui language bottom floating slide up dropdown link item">
 				{{svg "octicon-globe"}}
-				<div class="text">{{.locale.LangName}}</div>
+				<span>{{.locale.LangName}}</span>
 				<div class="menu language-menu">
 					{{range .AllLangs}}
 						<a lang="{{.Lang}}" data-url="{{AppSubUrl}}/?lang={{.Lang}}" class="item {{if eq $.locale.Lang .Lang}}active selected{{end}}">{{.Name}}</a>