[llvm] [VPlan] Expand VPWidenIntOrFpInductionRecipe into separate recipes (PR #118638)

[Luke Lau via llvm-commits]

lukel97 wrote:

I've updated this PR to remove the need for a custom phi recipe, and instead reuse VPWidenPHIRecipe, which also requires #120338.

Now there should only be two extra recipes needed here, one to model step vectors and another to model splats.

https://github.com/llvm/llvm-project/pull/118638