[llvm] [AArch64] Extend usage of `XAR` instruction for fixed-length operations (PR #139460)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Thanks - nice work. This looks good (it gets a bit fiddly with all the combos), but I think the smaller types need to be expanding to vectors with the same element sizes to make sure the rotates operate correctly.

https://github.com/llvm/llvm-project/pull/139460