ChatRoomMessagePriority constructor Null safety

1. agora_chat_sdk
2. agora_chat_sdk
3. ChatRoomMessagePriority
4. ChatRoomMessagePriority const constructor

ChatRoomMessagePriority enum

1. Constructors
2. ChatRoomMessagePriority
3. Values
4. High
5. Normal
6. Low
7. Properties
8. hashCode
9. index
10. runtimeType
11. Methods
12. noSuchMethod
13. toString
14. Operators
15. operator ==
16. Constants
17. values