EnginePhase constructor Null safety

1. Flutter
2. flutter_test
3. EnginePhase
4. EnginePhase const constructor

EnginePhase enum

1. Constructors
2. EnginePhase
3. Values
4. build
5. layout
6. compositingBits
7. paint
8. composite
9. flushSemantics
10. sendSemanticsUpdate
11. Properties
12. hashCode
13. index
14. runtimeType
15. Methods
16. noSuchMethod
17. toString
18. Operators
19. operator ==
20. Constants
21. values