Make YaPluginFactory abstract

And add separate implementations for the native plugin and the Wine
plugin host. This way we can easily allow the native host to do
callbacks without having to manage a load of lambdas.

src/common/serialization/vst3/plugin-factory.cpp

@@ -119,24 +119,6 @@ tresult PLUGIN_API YaPluginFactory::getClassInfo(Steinberg::int32 index,
     }
 }
 
-tresult PLUGIN_API
-YaPluginFactory::createInstance(Steinberg::FIDString /*cid*/,
-                                Steinberg::FIDString /*_iid*/,
-                                void** /*obj*/) {
-    // TODO: Figure out how to implement this. Some considerations:
-    //       - We have to sent a control message to the Wine plugin host to ask
-    //         it to create an instance of `_iid`.
-    //       - We then create a `Ya*` implementation of the same interface on
-    //         the plugin side.
-    //       - These two should be wired up so that when the host calls a
-    //         function on it, it should be sent to the instance on the Wine
-    //         plugin host side with the same cid.
-    //       - We should have a list of interfaces we support. When we receive a
-    //         request to create an instance of something we don't support, then
-    //         we should log that and then fail.
-    return 0;
-}
-
 tresult PLUGIN_API
 YaPluginFactory::getClassInfo2(int32 /*index*/,
                                Steinberg::PClassInfo2* /*info*/) {
@@ -150,10 +132,3 @@ YaPluginFactory::getClassInfoUnicode(int32 /*index*/,
     // TODO: Implement
     return 0;
 }
-
-tresult PLUGIN_API
-YaPluginFactory::setHostContext(Steinberg::FUnknown* /*context*/) {
-    // TODO: I guess this should do a callback and set the Wine host's host
-    //       context, right?
-    return 0;
-}