[llvm] [VPlan] Simplify reverse(reverse(x)) -> x (PR #199057)

[Luke Lau via llvm-commits]

lukel97 wrote:

@Mel-Chen glad to see https://github.com/llvm/llvm-project/pull/199510 got landed, rebased on top and moved the transform to VPlanTransforms::optimize.

https://github.com/llvm/llvm-project/pull/199057