ConnectionManager constructor Null safety

1. sendbird_sdk
2. connection_manager
3. ConnectionManager
4. ConnectionManager constructor

ConnectionManager class

1. Constructors
2. ConnectionManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Static methods
12. flushCompleters
13. readyToExecuteAPIRequest
14. readyToExecuteWSRequest