[llvm] [LV] Rework legacy widen/replicate in tryToBuildVPlan (NFC) (PR #224569)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

This is a very nice clean up, thanks!

Non-RPOT should be fine, as the code now just does RAUW

https://github.com/llvm/llvm-project/pull/224569