[llvm] [VectorCombine] Fold ZExt/SExt (Shuffle (ZExt/SExt %src)) to ZExt/SExt (Shuffle %src). (PR #141109)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> No objections, my only thought is why its in VectorCombine and not InstCombine if it isn't cost/target driven?

@RKSimon I think this should probably be limited to cases where the cost of the new extend isn't worse than the 2 separate extends. Added a check

https://github.com/llvm/llvm-project/pull/141109