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>

templates/shared/actions/runner_list.tmpl

@@ -20,9 +20,9 @@
 					</div>
 					<div class="ui input">
 						<input type="text" value="{{.RegistrationToken}}">
-						<div class="ui basic label button" data-clipboard-text="{{.RegistrationToken}}">
+						<button class="ui basic label button" aria-label="{{.locale.Tr "copy"}}" data-clipboard-text="{{.RegistrationToken}}">
 							{{svg "octicon-copy" 14}}
-						</div>
+						</button>
 					</div>
 					<div class="divider"></div>
 					<div class="item">

templates/shared/secrets/add_list.tmpl

@@ -1,7 +1,7 @@
 <h4 class="ui top attached header">
 	{{.locale.Tr "secrets.secrets"}}
 	<div class="ui right">
-		<div class="ui primary tiny show-panel button" data-panel="#add-secret-panel">{{.locale.Tr "secrets.creation"}}</div>
+		<button class="ui primary tiny show-panel button" data-panel="#add-secret-panel">{{.locale.Tr "secrets.creation"}}</button>
 	</div>
 </h4>
 <div class="ui attached segment">