[TASK] Make ActionController abstract

Since there is no dedicated AbstractController any more and
ActionController cannot be dispatched without being extended
the class is finally marked abstract.

Releases: master
Resolves: #92850
Change-Id: I910765ded482a59789dc3830701e497b4b8b45b8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66642


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>