[red-knot] Improve chained comparisons handling (#13825)
## Summary
A small fix for comparisons of multiple comparators.
Instead of comparing each comparator to the leftmost item, we should
compare it to the closest item on the left.
While implementing this, I noticed that we don’t yet narrow Yoda
comparisons (e.g., `True is x`), so I didn’t change that behavior in
this PR.
## Test Plan
Added some mdtests 🎉
