[llvm] [NewPM] Port x86-pad-short-functions to new PM (PR #190886)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

I think an Impl class makes more sense here given there is some state that gets moved around (i.e., VisitedBBs)?

https://github.com/llvm/llvm-project/pull/190886