ChatPresenceManagerListener constructor Null safety

1. agora_chat_sdk
2. agora_chat_sdk
3. ChatPresenceManagerListener
4. ChatPresenceManagerListener constructor

ChatPresenceManagerListener class

1. Constructors
2. ChatPresenceManagerListener
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. onPresenceStatusChanged
9. toString
10. Operators
11. operator ==