Pass struct hlsl_constant_value to folding functions, in preparation for creating the destination constant instruction from that value.
-- v2: vkd3d-shader/hlsl: Pass hlsl_constant_value and hlsl_type pointers to fold_nequal(). vkd3d-shader/hlsl: Pass hlsl_constant_value and hlsl_type pointers to fold_mul(). vkd3d-shader/hlsl: Pass hlsl_constant_value and hlsl_type pointers to fold_add(). vkd3d-shader/hlsl: Pass hlsl_constant_value and hlsl_type pointers to fold_neg(). vkd3d-shader/hlsl: Pass hlsl_constant_value and hlsl_type pointers to fold_cast().