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
#23337 (comment),
`<a>`s without `href` attribute are not focusable.
They should later on be converted to `<button>`s.

---------

Co-authored-by: wxiaoguang <[email protected]>
Co-authored-by: silverwind <[email protected]>
Co-authored-by: techknowlogick <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>

Author: 5 people

public/img/svg/fontawesome-save.svg

@@ -433,7 +433,7 @@
 
 				<div class="field">
 					<button class="ui green button">{{.locale.Tr "admin.auths.update"}}</button>
-					<div class="ui red button delete-button" data-url="{{$.Link}}/delete" data-id="{{.Source.ID}}">{{.locale.Tr "admin.auths.delete"}}</div>
+					<button class="ui red button delete-button" data-url="{{$.Link}}/delete" data-id="{{.Source.ID}}">{{.locale.Tr "admin.auths.delete"}}</button>
 				</div>
 			</form>
 		</div>