Add ANN200 error for "Function returns Any"

[silasary]

Description
Marking a function as -> Any is effectively the same as not having an annotation at all. There should be an error reporting such annotations.

[sco1]

I think a case can be made to add an opinonated. off by default, warning (a la mypy's dynamic typing options). I'm not sure there's a reason to limit it to just return annotations.