[BUGFIX] (Reflection): Prevent use of ReflectionService for Doctrine Proxies
When calling the ReflectionService with a class name for a doctrine proxy,
really weird side-effects can happen, as the Doctrine Proxy class is then
also stored in the Reflection Cache. On the next compilation run, really
weird side-effects can happen. See the corresponding issue for a full
By throwing an exception when a doctrine class is reflected, we prevent
the issue from appearing in the first place.