stubgen: Add support for yield statements

[srittau]

Description

Stubgen: Support functions that yield values:

def foo():
    x = yield 123
    return ""
def bar():
    yield

will be generated as:

from collections.abc import Generator
from typing import Any

def foo() -> Generator[Any, Any, Any]: ...
def bar() -> Generator[None, None, None]: ...

Before this change, these function were annotated with a None return type.

This PR doesn't support yield from expressions (see #10744).

Test Plan

Tests for this feature and a few corner cases were added.

[srittau]

The name typing_name is not really correct anymore, since we use it for collections.abc as well. Should we rename it?

[JelleZijlstra]

I don't feel strongly, it's still a typing concept even if it lives in collections.abc.

[srittau]

Gentle pingedy pong.

[JelleZijlstra]

Thanks! I even ran into this when writing the beautifulsoup stubs the other day :)