[llvm] [LV][TTI] Calculate cost of extracting last index in a scalable vector (PR #144086)

[David Sherwood via llvm-commits]

david-arm wrote:

Hopefully I've addressed everyone's comments with the new version of the hook - getVectorInstrCostFromEnd. I just noticed a conflict so I'll rebase the PR.

https://github.com/llvm/llvm-project/pull/144086