Improve styling of backend function menu

[christianbltr]

The function menu in the backend module should be improved to better match the styling of the other modules (e. g. the "info" module).

[ayacoo]

Besides the actual template in ke_search, the core, too, would probably have to be adapted. In typo3/sysext/fluid/Classes/ViewHelpers/Be/Menus/ActionMenuViewHelper.php the Bootstrap 5 css classes for the select tag are missing.

[christianbltr]

The backend module function menu had been improved when the extension had been made compatible with TYPO3 12, so I'm closing this.