[3.6] bpo-28556: typing.get_type_hints: better globalns for classes and modules ...

[3.6] bpo-28556: typing.get_type_hints: better globalns for classes and modules (GH-3582) (#3583)

This makes the default behavior (without specifying `globalns` manually) more
predictable for users, finds the right globalns automatically.

Implementation for classes assumes has a `__module__` attribute and that module
is present in `sys.modules`.  It does this recursively for all bases in the
MRO.  For modules, the implementation just uses their `__dict__` directly.

This is backwards compatible, will just raise fewer exceptions in naive user
code.

Originally implemented and reviewed at https://github.com/python/typing/pull/470.
(cherry picked from commit f350a268a7071ce7d7a5bb86a9b1229782d4963b)