Debug adapter logging can cause high CPU when there's lots of VM Service traffic

[DanTup]

Given an app that spawns isolates every half second:

void main() {
  runApp(const MyApp());
  Timer.periodic(const Duration(seconds: 1), (timer) async {
    final res = await Isolate.run(() => comp(100, 200));
  });
}

The CPU usage of the VS Code "window" process goes very high. It seems to be related to the volume of the dart.log events coming back from the debug adapter.

Right now, this logging is always enabled (so you can start logging after the debug session has started), but since this can negatively affect performance we should enable it only if logging is enabled as the debug session starts. If this becomes a problem, we should add the ability to send a custom message to the DA to start/stop logging later.