Format constructor Null safety

1. face_sdk
2. face_sdk
3. Format
4. Format const constructor

Format enum

1. Constructors
2. Format
3. Values
4. FORMAT_GRAY
5. FORMAT_RGB
6. FORMAT_BGR
7. FORMAT_YUV_NV21
8. FORMAT_YUV_NV12
9. Properties
10. hashCode
11. index
12. runtimeType
13. Methods
14. noSuchMethod
15. toString
16. Operators
17. operator ==
18. Constants
19. values