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

[David Sherwood via llvm-commits]

david-arm wrote:

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

Yep, you're absolutely right! And it was me that landed the cost model patch for ExtractFirstActive. :face_palm I've rebased it now.

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