Function calculate_state_changes 

async fn calculate_state_changes<'a>(
    services: &Services,
    sender_user: &UserId,
    room_id: &RoomId,
    full_state: bool,
    use_state_after: bool,
    since_shortstatehash: Option<ShortStateHash>,
    horizon_shortstatehash: Option<ShortStateHash>,
    after_shortstatehash: Option<ShortStateHash>,
    current_shortstatehash: ShortStateHash,
    joined_since_last_sync: bool,
    witness: Option<&'a Witness>,
) -> Result<StateChanges>