Provide a clearer message if a user connects to a DartVM that isn't connected to Flutter Tools.

From a user on discord:

> Today, i tried something new...
> i ran an android app with a view in flutter (add-to-app) and observed that when the FlutterEngine is initialised, i get a log saying flutter: Observatory listening on http://127.0.0.1:38177//. I tried to open this in Flutter Devtools (by installing Termux, exposing this port to the internet using ngrok and opening this in Devtools) but got a message saying "This application does not have any tabs".
> What is different when the app is run using flutter run and when the debug apk is run? if there is no way to open the observatory, why the log?

The problem is the Dart VM likely cannot evaluate expressions as Flutter tools isn't attached to it. We see this combined with a VM that appears to be debug mode and get confused and show zero tabs instead of showing a message like "VM Service not fully initialized, run `flutter attach` so that you can debug.

Comienza rastreando el manejo del mensaje "This application does not have any tabs" cuando una Dart VM no está completamente conectada a Flutter Tools. Confirma el estado de inicialización del VM-service y actualiza el resultado visible para el usuario para explicar que se requiere `flutter attach`; se considera terminado cuando este caso ya no aparece como un conjunto de pestañas vacío.

Escrito por el modelo de indexación a partir del texto del issue.