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

[elliette]

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