[TASK] Migrate `getMockForAbstractClass()` calls in `EXT:core`

`getMockForAbstractClass` has been (soft-)deprecated in PHPUnit 10.1:
https://github.com/sebastianbergmann/phpunit/issues/5241

Hence, we should replace its usages to follow best practices and
avoid deprecation warnings later with PHPUnit 11.

We do this by creating dedicated fixture subclasses of the affected
abstract classes.

Resolves: #101666
Related: #101601
Releases: main, 12.4
Change-Id: I0263ff7b0639d72ba1d4f30e3bee12276d364591
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80946


Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>