Send the factory from the Wine host to the plugin

src/common/serialization/vst3.h

@@ -50,7 +50,9 @@ struct WantsConfiguration {
  * copy of the hosted Windows VST3 plugin's `IPluginFactory{,2,3}` interface.
  */
 struct WantsPluginFactory {
-    using Response = YaPluginFactory;
+    // TODO: Some things had to be changed to use references since this is an
+    //       abstract class. Check if nothing breaks.
+    using Response = YaPluginFactory&;
 };
 
 /**