[InstCombine] add DeMorgan folds for logical ops in select form

We canonicalized to these select patterns (poison-safe logic)
with D101191, so we need to reduce 'not' ops when possible
as we would with 'and'/'or' instructions.

This is shown in a secondary example in:
https://llvm.org/PR50389

https://alive2.llvm.org/ce/z/BvsESh