Array after array_push / array_unshift call can still be empty

[herndlm]

Closes phpstan/phpstan#7424

The problem was that ArrayType::setOffsetValueType always makes arrays non-empty, which is not wanted in this case (if optional is true in the callback). And the solution here for simplicity reasons is to basically remove NonEmptyArrayType from the result again if either optional is false or the original array was already not iterable at least once before setting the offset.
An alternative might be to add an $optional arg to setOffsetValueType, but I'm not sure about the impact of that yet.

[ondrejmirtes]

Yeah, I guess this is fine :) Any reason why it's still a draft?

[herndlm]

Wanted to see if there's a better solution, e.g. for removing non-empty-array or in general for setting optional offsets. But I guess it's fine them for now

[ondrejmirtes]

There's always a cleaner solution by providing a new Type method on all implementations, but then you need to implement it on all Types obviously :D So this is fine :)

[ondrejmirtes]

Thank you!

[herndlm]

I remember there was only one failure yesterday. Rebased just in case this fixes something :)