Function outer_general 

fn outer_general(
    fun: &RValue,
    x_items: &[RValue],
    y_items: &[RValue],
    nx: usize,
    ny: usize,
    x_orig: &RValue,
    y_orig: &RValue,
    context: &BuiltinContext<'_>,
    env: &Environment,
) -> Result<RValue, RError>

General outer product: call FUN(x_i, y_j) for each pair and collect into a matrix.