[Clang][SVE] Change LLVM representation of ACLE tuple types to be struct based. (#108008)
This implements our original design now that LLVM is comfortable with
structs and arrays of scalable vector types. All SVE ACLE intrinsics
already use struct types so the effect of this change is purely the
types used for alloca and function parameters.
There should be no C/C++ user visible change with this patch.