[llvm] [LV] Allow scalable VFs in `-force-vector-width` (and use in tests) (PR #204953)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

I think `UFVScaleUserBeforeMaterialization` should no longer be needed and can also be removed?

https://github.com/llvm/llvm-project/pull/204953