watchdog(): Check if container exists, to avoid fatal error on Drupal::request() if in early bootstrap.
Watchdog should just print, if there is no container.
AnnotatedClassDiscovery with PSR-4 style directories.
Introduce AbstractAnnotatedClassDiscovery
Change the way that annotation namespaces are added to AnnotatedClassDiscovery. Introduce addAnnotationNamespace().
change constructor signature of DefaultPluginManager, and give it an addAnnotationClass() method.