Refactor branch/tag selector dropdown (first step) (#23394)

Follow: 
* #23345

The branch/tag selector dropdown mixes jQuery/Fomantic UI/Vue together,
it's very diffcult to maintain and causes unfixable a11y problems. It
also causes problems like #19851 #21314 #21952

This PR is the first step for the refactoring, move `data-` attributes
to JS object and use Vue data as much as possible.

The old selector `'.choose.reference .dropdown'` was also wrong, it hits
`<div class="choose reference"><svg class="dropdown icon">` and would
cause undefined behaviors.

I have done some quick tests and it works. After this PR gets merged, I
will move the code into a Vue SFC in next PR.



![image](https://user-images.githubusercontent.com/2114189/224099638-378a8a86-0865-47d1-bcba-f972506374c7.png)


![image](https://user-images.githubusercontent.com/2114189/224099690-70276cf5-b1e4-404a-b0c6-582448abf40e.png)

---------

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/js/features/repo-legacy.js

@@ -485,7 +485,7 @@ export function initRepository() {
   // File list and commits
   if ($('.repository.file.list').length > 0 || $('.branch-dropdown').length > 0 ||
     $('.repository.commits').length > 0 || $('.repository.release').length > 0) {
-    initRepoBranchTagDropdown('.choose.reference .dropdown');
+    initRepoBranchTagDropdown('.choose.reference .ui.dropdown');
   }
 
   // Wiki