[llvm] [LV]: Add costs to VPInstruction (PR #125008)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Could you please add a test case, some more details of what VPInstructions need costs now and how this is related to the change for interleaving?

https://github.com/llvm/llvm-project/pull/125008