[analyzer][solver][NFC] Refactor how we detect (dis)equalities

This patch simplifies the way we deal with (dis)equalities.
Due to the symmetry between constraint handler and range inferrer,
we can have very similar implementations of logic handling
questions about (dis)equality and assumptions involving (dis)equality.

It also helps us to remove one more visitor, and removes uncertainty
that we got all the right places to put `trackNE` and `trackEQ`.

Differential Revision: https://reviews.llvm.org/D105693