[llvm] `llvm.canonicalize` in common code (PR #142105)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > Patch title is now less clear, this is DAG codegen support
> 
> So, something like "DAG codegen support for `llvm.canonicalize`"?

How about "[DAG] Add generic expansion for ISD::FCANONICALIZE nodes"?

The summary description still needs work

https://github.com/llvm/llvm-project/pull/142105