Fix TypeCombinator::union() for intersection of array and template type

[rvanvelzen]

Fixes phpstan/phpstan#4117

[ondrejmirtes]

Thank you!

[ondrejmirtes]

I've added a type inference test: 98ab8c9

I think that the results in if/else are correct, but the type below the if/else should be better because it has subtracted falsy values but in fact the returned type can still be falsy. (The union of the types inside if/else is probably wrong).

[AJenbo]

Nice work :)