[TASK] Harden \TYPO3\CMS\Extbase\SignalSlot\Dispatcher

- Use strict type mode
- Use type hints whereever possible

Releases: master
Resolves: #87604
Change-Id: Iab0fbcd4594d2c4c27846566b6e72fe97e40ec8d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/59599


Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>