[llvm] [VPlan] Implement VPExtendedReduction, VPMulAccumulateReductionRecipe and corresponding vplan transformations. (PR #137746)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

@fhahn apologies for the prod, but could you give this another look? There are several other PRs that are gated by this one, so it would be great to see this land so the follow-up work can make some progress.

https://github.com/llvm/llvm-project/pull/137746