SemanticsOwner constructor Null safety

1. Flutter
2. semantics
3. SemanticsOwner
4. SemanticsOwner constructor

SemanticsOwner class

1. Constructors
2. SemanticsOwner
3. Properties
4. hashCode
5. hasListeners
6. rootSemanticsNode
7. runtimeType
8. Methods
9. addListener
10. dispose
11. noSuchMethod
12. notifyListeners
13. performAction
14. performActionAt
15. removeListener
16. sendSemanticsUpdate
17. toString
18. Operators
19. operator ==