Feature request

• I suspect this phpstan/phpstan-src@d281214 might have broken levels handling. I expect this behaviour so it should be tested and fixed:
  • array<string, X> going into list<X> should be reported on level 3 - it can never be true. This needs to be tested on property assignments.
  • array<int, X> going into list<X> needs to be reported on level 7
  • list<string|null> going into list<string> needs to be reported on level 8
• I suspect there might something wrong with covariance checking. Basically list<string> is a subtype of array<int, string>. So in parent method return type if there's array<int, string> and list<string> in a child class it should not be reported
  • But if there's list<string> in parent method and array<int, string> in child method then it should be reported.
  • If it already works correctly there should still be a test for this.
• Test for things I mentioned in comment Implement array list type phpstan-src#1751 (review). The AccessoryArrayListType::unsetOffset() is wrong I think in regard to what I said about unset.