[Inspector UXR] Visual link between widget tree and layout explorer

_This issue has been broken out of https://github.com/flutter/devtools/issues/2890_

## Visual link between widget tree and layout explorer

There’s currently no visual link between the widget tree and layout explorer. We also feel the coloring of the Flutter Inspector might be confusing for users.

### Suggestions

* Matching the colors of the layout explorer and details tree with the opened widget in the widget tree
* Other ways of color matching such as different widgets or widget families

首先查看父 issue #2890 和附带的屏幕截图，以了解现有的 widget 树、布局浏览器和 Inspector 的呈现方式。在实现之前，定义并就具体的视觉链接设计达成一致；完成应包括使已打开的 widget 在相关视图之间保持匹配，或以其他方式建立清晰的关联，并解决颜色方面的问题。

由索引模型根据 Issue 内容生成。