Pass through host provided IBStream objects

So if the host supports IStreamAttributes, we can also provide objects
that support the same itnerface to the plugin.

src/common/serialization/vst3/plugin/xml-representation-controller.h

@@ -96,11 +96,13 @@ class YaXmlRepresentationController
         native_size_t instance_id;
 
         Steinberg::Vst::RepresentationInfo info;
+        YaBStream stream;
 
         template <typename S>
         void serialize(S& s) {
             s.value8b(instance_id);
             s.object(info);
+            s.object(stream);
         }
     };