Feature: #96041 - Improve Backend toolbar registration

See Issue #96041

Description

The toolbar in the TYPO3 backend is well known by users as it provides e.g. the personal bookmarks or a common used feature for administrators: the “flush caches” action.

It’s furthermore also possible for extension authors to add their own toolbar items. The registration therefore had to be done in the LocalConfiguration.php file.

Since the introduction of the symfony service container in TYPO3 v10, it’s possible to autoconfigure services. This feature is now also used for the toolbar items. Therefore, the previous registration step is now superfluous. All toolbar items are now automatically tagged and registered based on the implemented ToolbarItemInterface.

Impact

Custom toolbar items are now automatically registered, based on the implemented interface, through the service configuration.