HLSL: various SPIR-V compute shader IDs must be a 3-vector of integers.

HLSL: various SPIR-V compute shader IDs must be a 3-vector of integers.

This PR forces the external definition of SV_GroupID variables to 3-vectors.
The conversion process between the shader-declared type and the external type
happens in wrapped main IO variable conversion.

The same applies to SV_DispatchThreadID and SV_GroupThreadID.

Fixes: #1371