Make adjustments to support PHP8.1's stricter type system

[nezaniel]

This adds additional type hints where required in PHP 8.1 while maintaining support for 7.4.
These are only the adjustments required fir the ESCR test suite, more are to follow

Resolves: #2698

[mficzel]

It would be great to add php 8.1 to the test matrix in .github/workflows/build.yml together with this.

[albe]

Looks good by reading, but I agree having 8.1 builds run would be good

[nezaniel]

8.1 builds are configured and run through smoothly, which leaves me a bit sceptical since that seems improbable. Is there more to be configured or is everything fine already?

[albe]

8.1 builds are configured and run through smoothly, which leaves me a bit sceptical since that seems improbable. Is there more to be configured or is everything fine already?

==> Setup PHP
✓ PHP Found PHP 8.1.2

Looks good to me. Are there any specific reasons why you think running Flow on 8.1 should not work with this PR applied @nezaniel ? Are there any breaking changes in 8.1 that we should be subject to?
I could very well imagine Flow being okay and Neos having a few more edge cases from a gut feeling

[mficzel]

i somehow miss the psalm test in the matrix now. Should offcourse not run on 7.3 but on 8.0 i think. Or was it disabled for not behaving well.

[nezaniel]

@albe Well, I had to un-proxy literally every ESCR exception class for it to not throw a __wakeup() signature notice, so I expected this to happen all over the Flow code base... but maybe the ESCR test setup is a little more strict than the regular tests and PHP runtimes

As far as I could see, the psalm tests were configured for 7.3 only, so I disabled them

[bwaidelich]

Looking good in general, I just added to nitpicky comments