Convert <div class="button"> to <button class="button"> (#23337)

This improves a lot of accessibility shortcomings.
Every possible instance of `<div class="button">` matching the command
`ag '<[^ab].*?class=.*?[" ]button[ "]' templates/ | grep -v 'dropdown'`
has been converted when possible.
divs with the `dropdown` class and their children were omitted as
1. more analysis must be conducted whether the dropdowns still work as
intended when they are a `button` instead of a `div`.
2. most dropdowns have `div`s as children. The HTML standard disallows
`div`s inside `button`s.
3. When a dropdown child that's part of the displayed text content is
converted to a `button`, the dropdown can be focused twice

Further changes include that all "gitea-managed" buttons with JS code
received an `e.preventDefault()` so that they don't accidentally submit
an underlying form, which would execute instead of cancel the action.
Lastly, some minor issues were fixed as well during the refactoring.

## Future improvements

As mentioned in
https://github.com/go-gitea/gitea/pull/23337#discussion_r1127277391,
`<a>`s without `href` attribute are not focusable.
They should later on be converted to `<button>`s.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

web_src/js/features/repo-issue.js

@@ -230,7 +230,8 @@ export function initRepoIssueStatusButton() {
     const value = easyMDE?.value() || $(this).val();
     $statusButton.text($statusButton.data(value.length === 0 ? 'status' : 'status-and-comment'));
   });
-  $statusButton.on('click', () => {
+  $statusButton.on('click', (e) => {
+    e.preventDefault();
     $('#status').val($statusButton.data('status-val'));
     $('#comment-form').trigger('submit');
   });