[TASK] Harden ExtbaseRequestParameters

ExtbaseRequestParameters is the old extbase request,
now a PSR-7 attribute. To continue with refactorings
in related areas, the @internal attribute is now hardened
with proper type hints and return values.
The properties receive some documentation love to finally
have a place where all the different state is documented
including some hopefully meaningful examples.

Resolves: #96292
Releases: main
Change-Id: I731aac221d804d56a3efe67de9eac65f785b5ab2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72559
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>