Fix crash on strict-equality with recursive types

[ilevkivskyi]

Fixes #16473

Potentially we can turn this helper function into a proper visitor, but I don't think it is worth it as of right now.

[AlexWaygood]

LGTM. One very minor code-style nit below:

[ilevkivskyi]

Right before merging this, I noticed there is a very similar crash that this PR would not fix. It is a bit trickier to fix, but generally the logic is the same.

Note btw that deciding whether two recursive types overlap is non-trivial, for example in the case with two different recursive Dicts, the overlap is a single element (an empty dict), so we give an error, similar to regular dicts/lists etc. But in case with two different recursive Lists the overlap is infinite: all kinds of lists of nested empty lists, like [[], [[], [[[]]]], []], so we don't give an error. It is not completely obvious that it is a desired behavior, but it would be weird to complain about non-overlapping comparison for types with infinite overlap.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅