[llvm] [CodeGen][Pass] Add `TargetPassBuilder` (PR #137290)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

I think this has been mostly superseded by the introduction of PMW/explicit nesting in the NewPM for CodeGen?

https://github.com/llvm/llvm-project/pull/137290