[llvm] [AArch64] Expand FORM_TRANSPOSED_REG_TUPLE to copies before regalloc (PR #207205)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm commented:

This approach makes sense to me; the only part that makes me a bit nervous is  the code that expands the tuple into scalar copies, especially around kill flags and liveranges (and subranges).

https://github.com/llvm/llvm-project/pull/207205