LegacyGlobalConfigurationAdapter should use externalizer ids from config

The LegacyGlobalConfigurationAdapter.adapt() method copies configuration from the legacy Infinispan GlobalConfiguration to the new style GlobalConfiguration. In doing so it attempts to add AdvancedExternalizers as-is, but this causes an NPE when the externalizer has not overridden the AbstractExternalizer.getId() method (which returns null) which is what happens for Externalizers added during ModuleLifecycles (e.g. the server externalizers)