[llvm] [VPlan] Compute cost for most opcodes in VPWidenRecipe (NFCI). (PR #98764)

[Florian Hahn via llvm-commits]

fhahn wrote:

@arcbbb what do you think about porting over the implementations from https://github.com/llvm/llvm-project/pull/67647, in particular the memory-op cost ones?

https://github.com/llvm/llvm-project/pull/98764