Consider optional keys in ConstantArrayType removeFirst and removeLast

[herndlm]

... and get rid of getConstantArrays in NodeScopeResolver for array_pop and array_shift.

This seems to be also fixing problems with the optional keys. green test cases from this PR for comparison with the latest 1.7.x state which is broken IMO
array_pop: https://phpstan.org/r/99745329-2125-46a3-8fe6-ea4afdfc754e
array_shift: https://phpstan.org/r/751ff62d-d672-4ef8-9db1-5abbb6cf4a15

The added tests show that apparently ArrayPopFunctionReturnTypeExtension and ArrayShiftFunctionReturnTypeExtension are not working correctly either ("should be" comments), but I'd like to look at that in another PR if that's ok. Maybe a bug somewhere else in ConstantArrayType itself 🤔 But I also have an idea for replacing those getConstantArrays calls as well.

My main motivation is to prepare stuff I can use in the ConstantArrayType::slice adaption. But now, since I learned that I can replace some of the potentially badly-scaling array gather & modify in a loop & unify code parts in general, I want to get rid of what I can :D

[herndlm]

should be ready. there were some random unrelated CI errors I never saw before, I'll force-push once more to retry and leave it then, as it is, to not burden the system more in case it is overloaded or whatever
UPDATE: sorry, just renamed something which bothered me :)

[herndlm]

hmm, the new composer integration error looks unrelated. I see that it's using a symfony lib in a version that was released literally minutes ago, which might be related :O

[ondrejmirtes]

Thank you!