[llvm] [VPlan] Introduce VPScalarPHIRecipe, use for can & EVL IV codegen (NFC). (PR #114305)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

Why we cannot create VPScalarPHIRecipe immediately instead of using it to replace some other (abstract) recipes?

https://github.com/llvm/llvm-project/pull/114305