Function to_vec_from_iter 

pub fn to_vec_from_iter<I, K, V>(
    iter: I,
    registry_type: (&Registry, TypeId),
) -> Result<Vec<u8>, Error>
where
    I: IntoIterator<Item = (K, V)>,
    K: Into<String>,
    V: Into<JsonValue>,

Like to_bytes_from_iter but allocates and returns a Vec<u8>.