[llvm] [VPlan] Simplify VPBlendRecipes to select instructions (PR #133993)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon approved this pull request.

Okay, I've convinced myself that this is a good direction, given the follow-up and context. I never really understood why we weren't lowering blends to primitive instructions, which are easier to reason about, in the first place. LGTM, pending on a second reviewer.

https://github.com/llvm/llvm-project/pull/133993