NERtcAudioFocusMode constructor Null safety

1. nertc
2. nertc
3. NERtcAudioFocusMode
4. NERtcAudioFocusMode constructor

NERtcAudioFocusMode class

1. Constructors
2. NERtcAudioFocusMode
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Constants
12. audioFocusGain
13. audioFocusGainTransient
14. audioFocusGainTransientExclusive
15. audioFocusGainTransientMayDuck
16. audioFocusOff