Look through invertible recurrences in isKnownNonEqual

This extends the phi handling in isKnownNonEqual with a special case based on invertible recurrences. If we can prove the recurrence is invertible (which many common ones are), we can recurse through the start operands of the recurrence skipping the phi cycle.

(Side note: Instcombine currently does not push back through these cases. I will implement that in a follow up change w/separate review.)

Differential Revision: https://reviews.llvm.org/D99912