[TASK] Harden \TYPO3\CMS\Extbase\Reflection\ClassSchema

- Use strict type mode
- Use type hints whereever possible

Releases: master
Resolves: #87940
Change-Id: I3f349d1cbb4ceec408de7e5d18cd1f0fc5cf4c7b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60277


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>