Implement IPlugFrame::resizeView()

The base IPlugFrame only contains this single function.

src/common/serialization/vst3.h

@@ -140,7 +140,8 @@ using CallbackRequest = std::variant<WantsConfiguration,
                                      YaComponentHandler::PerformEdit,
                                      YaComponentHandler::EndEdit,
                                      YaComponentHandler::RestartComponent,
-                                     YaHostApplication::GetName>;
+                                     YaHostApplication::GetName,
+                                     YaPlugFrame::ResizeView>;
 
 template <typename S>
 void serialize(S& s, CallbackRequest& payload) {

src/common/serialization/vst3/plug-frame/plug-frame.h

@@ -61,6 +61,28 @@ class YaPlugFrame : public Steinberg::IPlugFrame {
 
     inline bool supported() const { return arguments.supported; }
 
+    /**
+     * Message to pass through a call to `IPlugFrame::resizeView` to the
+     * `IPlugView` object provided by the host.
+     *
+     * XXX: Since we don't support multiple `IPlugView`s right now (as it's not
+     *      used the SDK's current version), we'll just assume that `view` is
+     *      the view stored in `Vst3PluginProxyImpl::plug_view`
+     */
+    struct ResizeView {
+        using Response = UniversalTResult;
+
+        native_size_t owner_instance_id;
+
+        Steinberg::ViewRect new_size;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.value8b(owner_instance_id);
+            s.object(new_size);
+        }
+    };
+
     virtual tresult PLUGIN_API
     resizeView(Steinberg::IPlugView* view,
                Steinberg::ViewRect* newSize) override = 0;