gh-138949: Fix non-generic children of generic TypedDicts with future annotations

[sobolevn]

This looks a bit messy, any suggestions on we can make this simplier are welcome.

It is really bad that TypedDict classes do not create correct __mro__ and just copies all annotations :(

• Issue: get_type_hints() fails on TypedDict inheriting from a generic TypedDict under PEP 563 #138949

[JelleZijlstra]

this seems wrong, base classes can have another type param with the same name

[JelleZijlstra]

This likely still returns wrong results and/or throws NameError if a stringified annotation refers to a (non-type param) name that is defined in the base class's module but not the child class's.

I think to do this fully correctly we'd have to add some data at TypedDict creation time: an annotation dict with just the TypedDict's own non-inherited annotations (own_annotations?) and the actual MRO (__typeddict_mro__?). The latter can already be reconstructed right now (as your code shows), but I don't think the former can be. It's not enough to e.g. look at which annotations exist in base classes, because the child class might override a base class annotation for the same name.