[FEATURE] PHP8.1 compatibility

[jpmschuler]

This is my current state of bugfixes that allows at least LIST/LATEST/SINGLE for a big legacy system.

It relies on TYPO3 v11.4.20, as AbstractPlugin is still not fully PHP8.1 compatible, see

• https://review.typo3.org/c/Packages/TYPO3.CMS/+/76598 (this can be hotfixed inside tt_news)
• https://review.typo3.org/c/Packages/TYPO3.CMS/+/76642
• https://review.typo3.org/c/Packages/TYPO3.CMS/+/76643

~I still got a small exception in my RSS feed, will add to this PR if that is resolved, but I think this here will already help a lot~ done

[jpmschuler]

Updated: RSS feed working, too.

[jpmschuler]

None of my systems generates any exceptions anymore, so I'm done with contributing to this PR

[jpmschuler]

closed in favour of #201