[InstSimplify] peek through 'not' operand in logic-of-icmps fold

This extends D78430 to solve cases like:
https://llvm.org/PR47858

There are still missed opportunities shown in the tests,
and as noted in the earlier patches, we have related
functionality in InstCombine, so we may want to extend
other folds in a similar way.

A semi-random sampling of test diff proofs in this patch:
https://rise4fun.com/Alive/sS4C