NERtcStreamFallbackOptions constructor Null safety

1. nertc
2. nertc
3. NERtcStreamFallbackOptions
4. NERtcStreamFallbackOptions constructor

NERtcStreamFallbackOptions class

1. Constructors
2. NERtcStreamFallbackOptions
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Constants
12. audioOnly
13. disabled
14. videoStreamLow