[llvm] [LV] Cost EVL width-adjusting zext/trunc as free (PR #225016)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Yeah, I have the same question when investigating the root cause. I can try to add overloaded return type for llvm.experimental.get.vector.length intrinsic !

Just noting that we do not necessarily have to adjust the intrinsic, we could also take care of this in the `ExplicitVectorLenght` VPInstruction, if we always want the cast considered free. 

https://github.com/llvm/llvm-project/pull/225016