[llvm] [VPlan] Reassociate (x & y) & z -> x & (y & z) (PR #155383)

[Mel Chen via llvm-commits]

https://github.com/Mel-Chen commented:

Why we don't generate `logical_and(header_mask, logical_and(mask1, mask2))` directly from the beginning, instead of relying on ::optimize?

https://github.com/llvm/llvm-project/pull/155383