[llvm] [VPlan] Use VPTypeAnalysis to get the step type of widen pointer induction (PR #147925)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> Hmm, wondering what the longer-term plan for `lv-strided-pointer-ivs` should be and if anybody is using it?

We've had this feature enabled by default in our internal branch for a long time to support RISC-V's strided segment accesses. That's why our tests were able to catch this bug.

https://github.com/llvm/llvm-project/pull/147925