[InstCombine] Refactor and/or of icmp with constant (NFCI)

Rather than testing for many specific combinations of predicates
and values, compute the exact icmp regions for both comparisons
and check whether they union/intersect exactly. If they do,
construct the equivalent icmp for the new range. Assuming that the
existing code handled all possible cases, this should be NFC.

Differential Revision: https://reviews.llvm.org/D113367