NERtcUserRole constructor Null safety

1. yunxin_roomkit
2. roomkit
3. NERtcUserRole
4. NERtcUserRole constructor

NERtcUserRole class

1. Constructors
2. NERtcUserRole
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Constants
12. audience
13. broadcaster