Fix get_class return type

[VincentLanglet]

Closes #2350
Closes phpstan/phpstan#4890

[ondrejmirtes]

I feel like a proper solution would be a new Type method. Basically the opposite of getClassStringObjectType. That one goes from class-string<Foo> to Foo.

We need to go from object Foo to class-string<Foo>.

And personally I don't think there's anything wrong with class-string<object{foo: Bar}> because it'd allow for a precise type when doing new on it again.

[VincentLanglet]

I feel like a proper solution would be a new Type method. Basically the opposite of getClassStringObjectType. That one goes from class-string<Foo> to Foo.

We need to go from object Foo to class-string<Foo>.

I introduced getClassStringType(), feel free to challenge the name :)

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

Would be nice to document what this is supposed to return similarly to how getClassStringObjectType and getObjectTypeOrClassStringObjectType are documented.

[VincentLanglet]

I added Return class-string<Foo> for object type Foo. ; is it enough ?