reconcile two arrays by intersecting them

[orklah]

This should fix #7469

This happened because there wasn't a dedicated code to handle an array existing type along with an array assertion

And given the two share the same getKey() value, it was weirdly handled.

This adds some specific code.

Not completely related to this PR: sometimes, we'll have to wonder what does TypeCombiner::combine really does. It's not the result of an union nor a result of an intersection. It kinda looks like the refineTypeWithAnother used somewhere else in the assertion module. I think the name is way better than combine and the way it works seems to be better too

[AndrolGenhald]

It's not the result of an union nor a result of an intersection.

If you're referring to combining array{a: int} and array{b: int} = array{a: int, b: int}, that actually is an intersection for unsealed arrays.

I know we haven't decided how to handle sealed arrays yet, but I've recently thought about implementing mapped types for arrays, so an unsealed array in Psalm 4 would be represented as array{a: int}, but in Psalm 5 (or maybe 6 at this point) it would be array{a: int, [array-key]: mixed}. This makes it much more intuitively obvious that array{a: int, [array-key]: mixed} & array{b: int, [array-key]: mixed} = array{a: int, b: int, [array-key]: mixed}, and it also allows for a lot of other cool things.

[orklah]

I think the syntax will need to be discussed with Ondrej, we don't want to create two standard on something this important I think

[AndrolGenhald]

I'll go comment on 5299, do we have somewhere else we're already coordinating with Ondrej or should I ping him?

Edit: Actually I see he already mentioned it here