Ensure that CacheKey is serializable across JVMs for entities with a composite primary key

The Infinispan L2 cache serializes the `CacheKey` instance and sends that to other nodes in the cluster to invalidate cache entries.  The `CacheKey` implements `Serializable`, but it is not always actually serializable.  When the `CacheKey` represents a composite primary key, the `type` variable is set to an instance of `EmbeddedComponentType`, which indirectly references `SessionFactoryImpl`.  While `SessionFactoryImpl` is serializable within a JVM, it is not serializable across JVMs.

See HHH-9424