[llvm] [NewPM][CodeGen] Add callback style codegen pass builder (PR #108690)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

sorry for the very slow review, will take a closer look soon

at a first glance, I'd really like to avoid `eraseIf` and either just don't add the passes in the first place or have the pass manager skip passes before/after ones we specify. and we shouldn't need it for the LLVM IR pass managers? LLVM IR passes can always be run individually so we shouldn't need to support start/stop-before/after on those.

still looking at the callbacks portion but in general I do think that is the direction to go

https://github.com/llvm/llvm-project/pull/108690