Handle page refreshes and opening in new tabs

[jakemac53]

Fixes #202

Note that I added an app instance id - this allows us to unambiguously identify the correct tab for a given instance of an app, separate from the app id which is consistent across all instances.

We cache the debug services per app ID and keep them running, but we only allow debugging one instance of a given app at a time.

The rough logic here is as follows:

• When a new client connects
  • if we have cached debug services for the app
    • if the old tab connection is still connected to the correct tab (page refresh case)
      • reconnect and create the new isolate
    • else
      • don't do anything
  • else
    • don't do anything
• When a client disconnects (from the SSE connection)
  • destroy the isolate (but leave the proxy services running).
• When a client sends a DevTools request
  • if we have an existing debug service for that app
    • if it is for the same app instance we are already debugging
      • open devtools tab pointing at the running debug services
    • else
      • alert the user that they can't debug the same app in multiple windows
  • else
    • create a new debug service for the app

[grouma]

Discussed offline. This does not handle the webdev daemon scenario as it currently tries to connect with the appId streamed from the devHandler. Initial thought is to unblock this PR by streaming the ConnectRequest and using the appId / appInstanceId inside app_domain.dart. We will follow up with another PR that reuses much of this logic inside app_domain.dart so that we properly handle full page refreshes.

[grouma]

Maybe add a comment that an instance in this case is one to one with a tab?

[jakemac53]

It changes if there is a refresh in the same tab though - it unique per instance of the app.