functools.partial should use PEP612 ParamSpec (depends on #8708)

Currently, functools.partial's __call__ method takes *args: Any, **kwargs: Any and returns _T (a TypeVar for the return type of the callable the partial is wrapping). This is decent, but matching the parameter typing would make this more useful in more situations.

I can sort of see how to deal with this, although I'll admit I'm unsure how to make this generically work. I imagine you could probably deal with some number of Concatenates (maybe up to 5 or 10) to deal with most cases. It's possible fixing this requires another PEP to allow an arbitrary-length Concatenate-type pattern.

Related to https://github.com/python/mypy/issues/1484

stdlib/functools.pyi の 75 行目付近から始め、PEP 612 の ParamSpec と Concatenate の概念を確認してください。要求された型付けを表現できるかどうかを判断する前に、issue #8708 と関連する mypy issue への依存関係を確認してください。完了の条件は、functools.partial の call が Any を使用するのではなく、ラップされた callable のパラメーターの型付けを維持することです。