ChatUserInfoManager constructor Null safety

1. agora_chat_sdk
2. agora_chat_sdk
3. ChatUserInfoManager
4. ChatUserInfoManager constructor

ChatUserInfoManager class

1. Constructors
2. ChatUserInfoManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. clearUserInfoCache
8. fetchOwnInfo
9. fetchUserInfoById
10. noSuchMethod
11. toString
12. updateUserInfo
13. Operators
14. operator ==