[llvm] [CodeGen] Port selection dag isel to new pass manager (PR #83567)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

> > Is there any npm-codegen channel/team that exists? I would be interested in getting a notification for PRs related to this.
> 
> Currently no, but there are indeed some people interested in related PRs, a new PR label would be good.

Yes, a label like backend::NewPM or backend::NPM would do.

https://github.com/llvm/llvm-project/pull/83567