Dart _HashMap class does not show the same debugger view as map #2723

To fix this and similar cases such as _HashSet and perhaps all classes implementing Map, Set, and Iterable
we should add helpers to Dart DevTools that use helpers to efficiently extra out the values from these fields by doing a single eval to convert over to the correct Dart List data to batch read the values.
Screenshot showing how this makes it hard to see the _inheritedWidgets for a Flutter class.