Some variables that are not expandable appear to be expandable

e.g., when inspecting the following:

```
final name = 'Prismo';
```

The little `>` makes it seem the variable is expandable:

Here is where we determine that: https://github.com/flutter/devtools/blob/0f72e7d300aa1d64f4fcee40ee2785e17cd069e1/packages/devtools_app/lib/src/shared/diagnostics/dart_object_node.dart#L269

从 packages/devtools_app/lib/src/shared/diagnostics/dart_object_node.dart 第 269 行附近开始，并使用提供的 final name 示例重现 inspector 的行为。跟踪如何为 Dart object nodes 选择可展开指示器。当不可展开的变量不再显示该指示器，而真正可展开的变量仍然显示时，即表示完成。

由索引模型根据 Issue 内容生成。