Use `RemoteDiagnosticNode.description` instead of `RemoteDiagnosticNode.widgetRuntimeType`

The JSON response for the widget tree currently contains a field titled `description` and a field titled `widgetRuntimeType`.

However, the `widgetRuntimeType` can be computed from the description, which is what we are currently doing in the Flutter Widget Inspector.

Examples:

Widget runtime type: `RootWidget`
description: `[root]`

Widget runtime type: `_InkFeatures`
description: `_InkFeatures-[GlobalKey#af894 ink renderer]`

从 Flutter Widget Inspector 中当前根据 RemoteDiagnosticNode.description 计算 widget 运行时类型的代码开始，追踪 JSON 字段的使用位置。更新 consumer，使其使用 description 而不是 widgetRuntimeType，然后验证显示的 widget 标签仍与此 issue 中的示例一致。

由索引模型根据 Issue 内容生成。