Fixes 'in' operator rejected with union type operand

[LiuYuHui]

Description

Fixes #4954

[msullivan]

Thanks for the PR!

This looks like it silences some issues:

w: Union[Container[str], int]
'x' in v

no longer produces an error.

I would try to avoid too much manual fiddling with local_errors. Maybe the thing to do is to extract most of the logic to a helper function and have it recurse in in the UnionType case.

[LiuYuHui]

@msullivan It seems like that this fix doesn't silence the case you mention, my thought is that split the original union type into two parts, one is that have __contains__, the other one is that don't have __contains__, and the next part will check if this one have 'in' operator. Do you know other way to find if the type have __contains__? It is the only way (use local_errors) I know.