NERoomEndReason constructor Null safety

1. yunxin_roomkit
2. roomkit
3. NERoomEndReason
4. NERoomEndReason const constructor

NERoomEndReason enum

1. Constructors
2. NERoomEndReason
3. Values
4. kLeaveBySelf
5. kSyncDataError
6. kKickOut
7. kSelfKick
8. kCloseByMember
9. kEndOfLife
10. kAllMemberOut
11. kCloseByBackend
12. kLoginStateError
13. kUnknown
14. Properties
15. hashCode
16. index
17. runtimeType
18. Methods
19. noSuchMethod
20. toString
21. Operators
22. operator ==
23. Constants
24. values