Previously `sve_cast`'s implementation was abstracted to power both
`sve_cast` and `simd_cast` which supported scalable and non-scalable
vectors respectively. In anticipation of having to do this for another
`simd_*` intrinsic, `sve_cast` is removed and `simd_cast` is changed to
accept both scalable and non-scalable intrinsics, an approach that will
scale better to the other intrinsics.
David Wood
ca6a85155b