The previous WaveActiveBallot implementation did not account for the
fact that the DXC implementation of the intrinsic returns a struct type
with 4 uints, rather than a vector of 4 uints. This must be respected,
otherwise the validator will reject the uses of WaveActiveBallot that
return a vector of 4 uints.
This PR updates the return type and adds the DXC-specific return type
`fouri32` to use for the intrinsic.
11b1836282