Function vec_t 

pub fn vec_t(
    n: usize,
    tplt_ty: &Type,
    args: &[Instance],
    stage: ShaderStage,
) -> Result<Instance, Error>

vecN<T>() constructor.

Expects tplt_ty to be valid (a scalar).

Reference: https://www.w3.org/TR/WGSL/#vec2-builtin