[llvm] [AArch64][SVE] Support lowering fixed-length BUILD_VECTORS to ZIPs (PR #111698)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

This PR is effectively expanding `BUILD_VECTOR` with custom shuffles and so I'm starting to wonder if we're at the point of reconsidering disabling `shouldExpandBuildVectorWithShuffles`.  This was initial done to simplify the path to SVE VLS code generation but at its core there was no other reason to disable it.

https://github.com/llvm/llvm-project/pull/111698