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

[via llvm-commits]

Michael-Chen-NJU wrote:

FYI this also fixes #199640, which is the same bug but with a narrower IV (i16 promoted to i32) where the stride exceeds INT32_MAX and the APInt constructor asserts directly.

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