[llvm] [VPlan] Improve narrowToSingleScalarRecipes (NFC) (PR #158427)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Using `RepOrWidenR` for both cases with cloning should help to denote that we are cloning the same thing.

If possiblem it would probably good to instead refactor so that there is only a single clone  needed

https://github.com/llvm/llvm-project/pull/158427