[llvm] [VPlan] Add VPInstruction::StepVector and use it in VPWidenIntOrFpInductionRecipe (PR #129508)

[David Sherwood via llvm-commits]

david-arm wrote:

It doesn't look the commit message now reflects the changes in the patch, since VPInstructionWithType seems to be already present in the code?

https://github.com/llvm/llvm-project/pull/129508