In ISPN-10354 we removed jboss-marshalling from the core and made JavaSerializationMarshaller the default user marshaller instead of JBossUserMarshaller. Consequently, externalizers are only respected by the GlobalMarshaller, meaning that when store's marshall objects via InitializationContext::getPersistenceMarshaller any user configured externalizers are not used for serialising user types.

We should provide a ExternalizerAwareSerializationMarshaller that first tries to serialize user types via any configured externalizers before defaulting to java Serialization.