Support `typing.get_type_hints(partial(fn, ...))` by 'unwrapping' the `partial`, and discarding hints for bound arguments

We added this to Hypothesis' get_type_hints() helper a few years ago, and while most of that function is clearly not suitable to upstream, it struck me recently that "works with functools.partial" could quite reasonably be added to the stdlib function.

It's also plausible that the typing module prefers to avoid calling inspect.signature, though I don't have a great sense of how to determine which parameters have been bound without getting the signature of the partial object. In any case, the implementation need not be the same as in Hypothesis, although as the author you're welcome to use that code if you'd like.

まず、既存の typing.get_type_hints の実装と、hypothesis-python/src/hypothesis/internal/compat.py で参照されている Hypothesis ヘルパーを読んでください。functools.partial と inspect.signature が束縛された引数をどのように公開するかを確認し、partial がアンラップされ、束縛された引数の型ヒントが破棄されることを示すテストを定義してください。既存の get_type_hints のケースを壊さずに、この動作がカバーされていれば完了です。