TypedDict with forward references do not work in argument conversion

[pekkaklarck]

If we use a TypedDict like below as a type hint, type conversion is done for key x but not for y.

from typing import TypedDict

class Example(TypedDict):
    x: int
    y: 'int'

This is different compared to functions and methods where argument conversion is done both for x and y if we have def example(x: int, y: 'int'). The reason is that with TypedDict the annotation assigned to y by Python is ForwardRef, while with functions and methods we get the original string. Our conversion logic handles strings as aliases but doesn't know that to do with ForwardRefs.

A simple fix for this issue is using typing.get_type_hints for getting types instead of accessing __annotations__ like we currently do. That has a problem that using something like x: 'int | float' will cause an error with Python < 3.10. We just added support for such stringified types in arguments (#4711) and supporting them with TypedDict would be good as well. I guess we need to use get_type_hints first and then access __annotations__ as a fall-back. Then we may get ForwardRefs and need to handle them as well.

[pekkaklarck]

This issue was initially reported by @aaltat on our Slack. He had used from __future__ import annotations instead of using stringified types, but that special import basically turns all annotations to strings and thus has the same effect.