[llvm] [VPlan] Add opcode to create step for wide inductions. (PR #119284)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Do we need to return true for WideIVStep in VPInstruction::onlyFirstLaneUsed if both inputs are scalar?

https://github.com/llvm/llvm-project/pull/119284