Implement the overload call site evaluation algorithm

[dhruvmanila]

Reference spec: https://typing.python.org/en/latest/spec/overload.html#overload-call-evaluation

[dhruvmanila]

I'm marking this as "Alpha" milestone because I want to try to implement some parts of it before then if possible otherwise the complete implementation would be completed before the "Beta" milestone. Happy to move it directly to "Beta" if other prefer.

Moved to beta as I don't think I'll have time to implement any part of it.

[JelleZijlstra]

Here's a concrete example of an issue with overloads I ran into trying out ty on some sample code:

from typing import reveal_type

def x(func):
    func = getattr(func, "__func__", func)
    reveal_type(func)

This produces Any | None but should be Any. Definition in typeshed for reference.

(Just mentioning this as an example that probably a good number of people trying out the alpha will run into.)