Widget inspector state is not cleared when navigating to new view in connected app

[elliette]

How to reproduce:

• Go into widget inspector mode
• Click on a widget to inspect
• Then, in the connect app, click on a widget what changes the view (I'm using the Flutter Gallery app)
• The widget inspector outlines from the old view are still present on the screen

See demo:

[jacob314]

Unfortunately this is a bit challenging to fix. Right now the json sent for each inspector tree is quite large so we are scared to manually dispatch new trees. To fix, we need to switch to a binary format for the inspector data and send a stream of data to the client to keep the tree truly up to date. Initial experiments suggest that with a binary format, we could handle keeping the client completely up to date with the server.