DelegatingMap class

1. Constructors
2. DelegatingMap
3. Properties
4. delegate
5. entries
6. isEmpty
7. isNotEmpty
8. keys
9. length
10. values
11. hashCode
12. runtimeType
13. Methods
14. addAll
15. addEntries
16. cast
17. clear
18. containsKey
19. containsValue
20. forEach
21. map
22. putIfAbsent
23. remove
24. removeWhere
25. retype
26. update
27. updateAll
28. noSuchMethod
29. toString
30. Operators
31. operator []
32. operator []=
33. operator ==