[TASK] Mark GeneralUtility as strict

This is the first step before we can start adding
native types to the GU methods in multiple separate
changes.

Resolves: #97578
Releases: main
Change-Id: I42e9da54b072f3c6d204ec5b8b32b797ab7996ec
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74572


Tested-by: core-ci <typo3@b13.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>