ConnectionEventHandler constructor Null safety

1. sendbird_sdk
2. connection_event_handler
3. ConnectionEventHandler
4. ConnectionEventHandler constructor

ConnectionEventHandler class

1. Constructors
2. ConnectionEventHandler
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. onReconnectionCanceled
9. onReconnectionFailed
10. onReconnectionStarted
11. onReconnectionSucceeded
12. toString
13. Operators
14. operator ==