Recognize Hashable as a real protocol, refs #11799

[sobolevn]

Sorry for spamming with PR, but this problem caught my eye 🙂

When this piece of code was checked:

from typing import Awaitable, Hashable, Union, Tuple, List

obj: Union[Tuple[int], List[int]]
if isinstance(obj, Hashable):
    reveal_type(obj)

Mypy revealed that Hashable is () -> object. It happened, because is_subtype(explicit_type, default_ret_type, ignore_type_params=True) was True, where explicit_type=object and default_ret_type=Hashable. It happened because object has __hash__ method.

The only thing that poped out of my head is to simply exclude protocols from this condition.
I guess that we might double check protocols with __new__ and __init__ to be sure. But, I am not able to think of proper test cases for this. Any ideas? Or is my single test good enough?

I am adding pythoneval test, because of the complexity in how Hashable is defined and analyzed in real life.

Closes #11799

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉