[TASK] Harden some DataHandler details

Check $dataMap and $commandMap structure in start(),
type hint them to array. This is considered b/w
compatible since DH would have failed already when
the incoming array shape was funny, and the annotations
clearly stated an array must be given for a long
time already.

Minor adaptions throughout DH class to happify
phpstan a bit more.

Change-Id: Idfc4b0c5c8db1b096f9477ce9b2bbfc0c5755a03
Resolves: #103213
Releases: main
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83073


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>