gh-111353: GenericAlias support and TypeVarLike resolution for `typing.get_type_hints`

[NCPlayz]

get_type_hints can now resolve TypeVarLikes correctly for all generic classes, including TypedDicts. There were a lot of edge cases that I tested and subsequently wrote unit tests for. I've also split some pre-existing code in the typing library into their own utility functions (_copy_with to work for copying any generic type with new params and _make_substitution from _GenericAlias._make_substitution).

I've tried my hardest to document each step but please let me know if there are any steps that don't make sense or could be written another way.

• Issue: gh-111353