[llvm] Reapply "[LV] Use ExtractLane(LastActiveLane, V) live outs when tail-folding. (#149042)" (PR #168738)

[Luke Lau via llvm-commits]

lukel97 wrote:

@fhahn I think all the prerequisites to relanding #149042 have now separately landed, do you still need this PR? Or do you want to directly commit the reapply

https://github.com/llvm/llvm-project/pull/168738