[TASK] Fix phpstan checkFunctionArgumentTypes errors in ext:core Charset

This patch fixes incompatible type usage in function arguments
and is preparatory work for introducing native type hints and
strict mode in all core files.

Releases: master, 10.4
Resolves: #92276
Change-Id: I28290de708946358794bfa73cac9c7c49ec1cc8b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65682


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Jörg Bösche <typo3@joergboesche.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>