Function user_can_see_summary 

async fn user_can_see_summary<'a, I>(
    services: &Services,
    room_id: &RoomId,
    join_rule: &JoinRuleSummary,
    guest_can_join: bool,
    world_readable: bool,
    allowed_room_ids: I,
    sender_user: Option<&UserId>,
) -> Result
where
    I: Iterator<Item = &'a RoomId> + Send,