Consider supporting an online "upgrade" experience when embedded in an IDE

In this scenario, I opened the Performance page in VS code when no debug sessions were available. This opened up the Performance screen for the "disconnected" state which allows the user to load offline data. I later ran a debug session, and still had the "offline" version of the Performance page.

It would be nice if a small banner popped up at the top of my performance tool that said something like
"A debug session is now available. Would you like to reload this tool and connect to it?". At that point the user could choose whether to ignore the message and continue looking at the offline data or reload the tool with the new app connection.

If the user chose to reload, DevTools could refresh itself so that the embedded IDE view would be reloaded. This would require the IDE to send an event to DevTools debug sessions change, and I think this event already exists because of the Flutter sidebar.

CC @DanTup @helin24