[llvm] [VPlan] Use pointer index type for stride in convertToStridedAccesses (PR #199647)

[via llvm-commits]

Michael-Chen-NJU wrote:

I've landed the pre-commit crash test in #200985.  Please rebase and update the test (remove not --crash, add proper CHECK lines) when ready.

https://github.com/llvm/llvm-project/pull/199647