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

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.

未指定文件或测试。首先定位 Dart DevTools 对 _HashMap 及其集合视图的调试器处理，然后查看如何通过一次求值批量读取值。完成的标准是：_HashMap、_HashSet 以及适用的 Map、Set 或 Iterable 实现都能提供有用的调试器视图，包括 _inheritedWidgets 情况。

由索引模型根据 Issue 内容生成。