Fix get_type_hints() on x-module inherited TypedDict in 3.9 and 3.10

[carljm]

The fix in python/cpython#27017 was never backported into typing-extensions.

In 3.11 it doesn't matter because we just use TypedDict from typing.py. But in 3.9 and 3.10, it means this cross-module inheritance scenario with stringified annotations and get_type_hints will fail if you use TypedDict from typing_extensions but work if you use it from typing.

I don't attempt here to backport the fix to pre-3.9 versions where typing.py doesn't have it; that would require pulling in lots more code (ForwardRef and some utility functions) into typing_extensions.py. Just aiming for parity with typing.py for 3.9 and 3.10.