GestureArenaManager constructor Null safety

1. Flutter
2. gestures
3. GestureArenaManager
4. GestureArenaManager constructor

GestureArenaManager class

1. Constructors
2. GestureArenaManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. add
8. close
9. hold
10. noSuchMethod
11. release
12. sweep
13. toString
14. Operators
15. operator ==