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/user/auth/grant.tmpl

@@ -23,7 +23,7 @@
 					<input type="hidden" name="scope" value="{{.Scope}}">
 					<input type="hidden" name="nonce" value="{{.Nonce}}">
 					<input type="hidden" name="redirect_uri" value="{{.RedirectURI}}">
-					<input type="submit" id="authorize-app" value="{{.locale.Tr "auth.authorize_application"}}" class="ui red inline button"/>
+					<button type="submit" id="authorize-app" value="{{.locale.Tr "auth.authorize_application"}}" class="ui red inline button">{{.locale.Tr "auth.authorize_application"}}</button>
 					<a href="{{.RedirectURI}}" class="ui basic primary inline button">Cancel</a>
 				</form>
 			</div>

templates/user/auth/webauthn_error.tmpl

@@ -17,6 +17,6 @@
 	</div>
 	<div class="actions">
 		<button onclick="window.location.reload()" class="success ui button gt-hidden webauthn_error_timeout">{{.locale.Tr "webauthn_reload"}}</button>
-		<div class="ui cancel button">{{.locale.Tr "cancel"}}</div>
+		<button class="ui cancel button">{{.locale.Tr "cancel"}}</button>
 	</div>
 </div>