File flickers in debugger during hot restart

If there are multiple isolates, like when vm mode is enabled, the file flickers when doing a hot restart.

This is because we switch to the other isolate while the main isolate restart. Then when it comes back up, we switch back to the main isolate.

This was originally introduced by fixing https://github.com/flutter/devtools/issues/5017

It didn't make sense to fully address this issue until we have a reliable way to determine if we are in the middle of a hot restart or not though.

As such we filed this issue, asking for events to to sent for the hot restart lifecycle. https://github.com/flutter/flutter/issues/134470

Once that issue has a resolution then we can develop a hot restart lifecycle state, and base a flickerless behaviour off of that.