[llvm] [NewPM][CodeGen] Port VirtRegMap to NPM (PR #109936)

[Akshat Oke via llvm-commits]

optimisan wrote:

### Merge activity

* **Oct 22, 5:41 AM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/109936).


https://github.com/llvm/llvm-project/pull/109936