[RFC][Pipeline] Avoid running transform passes that have just been run

[aeubanks]

@programmerjake

note InstCombine was changed to not always satisfy P(P(x)) == P(x):

[InstCombine] Only perform one iteration · llvm/llvm-project@4189584 · GitHub

The intent is still that instcombine is idempotent, and cases where it is not are rare and likely not very important. So we should still do this for instcombine.