[PassManager] Save compile time by not running the verifier unnecessarily. NFC

This changes the pass manager to not rerun the verifier when a pass says it
didn't change anything or after an OpToOpPassAdaptor, since neither of those
cases need verification (and if the pass lied, then there will be much larger
semantic problems than will be caught by the verifier).

This maintains behavior in EXPENSIVE_CHECKS mode.

Differential Revision: https://reviews.llvm.org/D104243