[llvm] [LV][NFC] Refactor code for extracting first active element (PR #131118)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Is it possible that this isn't based on the latest `main`? I am not seeing updates to `VPInstruction::computeCost`, which should handle `ExtractFirstActive`?

https://github.com/llvm/llvm-project/pull/131118