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

[Luke Lau via llvm-commits]

lukel97 wrote:

Gentle ping, I've reworked this PR since it no longer seems to depend on https://github.com/llvm/llvm-project/pull/133977 now that there's an extra run of simplifyRecipes after simplifyBlends. 

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