This is to achieve a clean separation of concerns - the watchdog is an inappropriate place for work management.
Also adds a WorkManager.RunInThreadPool() class which feeds through to Util.FireAndForget.
Also switches around the name and obj arguments to the new RunInThread() and RunJob() methods so that the callback obj comes after the callback as seen in the SDK and elsewhere
On the first frame, all startup scene objects are added to the physics scene.
This can cause a considerable delay, so we don't start raising the alarm on scene loop timeouts until the second frame.
This commit also slightly changes the behaviour of timeout reporting.
Previously, a report was made for the very first timed out thread, ignoring all others until the next watchdog check.
Instead, we now report every timed out thread, though we still only do this once no matter how long the timeout.
