[TASK] Add possibility creating accessible mock for abstract classes

Resolves: #53564
Releases: 6.0, 6.1, 6.2
Change-Id: If7d69e4f87e368c1eef672cb68f1af92d6ae501b
Reviewed-on: https://review.typo3.org/27252
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind