Fix false negatives in Y018/Y046/Y047/Y049

[AlexWaygood]

Fixes #383

[AlexWaygood]

⚠ Flake8 diff showing the effect of this PR on typeshed:

> ./stdlib/asyncio/__init__.pyi:39:5: Y047 Type alias "_AwaitableLike" is not used
> ./stdlib/asyncio/__init__.pyi:40:5: Y047 Type alias "_CoroutineLike" is not used

These are true positives: the aliases aren't used in that file: https://github.com/python/typeshed/blob/2d5dafadb75f122e0c2aeced09a5b72232373f40/stdlib/asyncio/__init__.pyi#L37-L43

[github-actions]

⚠ Flake8 diff showing the effect of this PR on typeshed:

> ./stdlib/asyncio/__init__.pyi:39:5: Y047 Type alias "_AwaitableLike" is not used
> ./stdlib/asyncio/__init__.pyi:40:5: Y047 Type alias "_CoroutineLike" is not used

[srittau]

I'm not a huge fan of defining field types in class scope, outside of their initialization. Feels not very Pythonic for me and duplicates code unnecessarily, but that's a personal preference, not a blocker.

[AlexWaygood]

I'm not a huge fan of defining field types in class scope, outside of their initialization. Feels not very Pythonic for me and duplicates code unnecessarily, but that's a personal preference, not a blocker.

I know what you mean. The reason I went this way was that the defaultdict annotations were getting too cumbersome otherwise. I couldn't stomach the idea of doing this five times in one __init__ method:

self.typevarlike_defs: defaultdict[TypeVarInfo, list[ast.Assign]]
self.typevarlike_defs = defaultdict(list)