[TASK] Decouple TreeController from UserSettingsController

Introduce a general wrapper for backend user configuration.

Resolves: #84353
Releases: master
Change-Id: Iddf01a18527ea732dc1c857e153880af57a492fd
Reviewed-on: https://review.typo3.org/56239


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>