Destroy IPlugFrame proxy together with IPlugView

Not that we have implemented `IPlugView::setFrame()` yet, but that
should be trivial at this point.

src/wine-host/bridges/vst3.cpp

@@ -22,6 +22,7 @@
 
 #include "vst3-impls/component-handler-proxy.h"
 #include "vst3-impls/host-context-proxy.h"
+#include "vst3-impls/plug-frame-proxy.h"
 
 InstanceInterfaces::InstanceInterfaces() {}
 
@@ -70,9 +71,13 @@ void Vst3Bridge::run() {
                 main_context
                     .run_in_context([&]() {
                         // When the pointer gets dropped by the host, we want to
-                        // drop it here as well
+                        // drop it here as well, along with the `IPlugFrame`
+                        // proxy object it may have received in
+                        // `IPlugView::setFrame()`.
                         object_instances[request.owner_instance_id]
                             .plug_view.reset();
+                        object_instances[request.owner_instance_id]
+                            .plug_frame_proxy.reset();
                     })
                     .wait();
 

src/wine-host/bridges/vst3.h

@@ -53,6 +53,16 @@ struct InstanceInterfaces {
      */
     Steinberg::IPtr<Vst3HostContextProxy> host_context_proxy;
 
+    /**
+     * If the host passes an `IPlugFrame` object during `IPlugView::setFrame()`,
+     * then we'll store a proxy object here and then pass it to
+     * `plug_view->setFrame()`. Will be initialized with a null pointer until
+     * used. When we destroy `plug_view` while handling
+     * `Vst3PlugViewProxy::Destruct`, we'll also destroy (our pointer of) this
+     * proxy object.
+     */
+    Steinberg::IPtr<Vst3PlugFrameProxy> plug_frame_proxy;
+
     /**
      * After a call to `IEditController::setComponentHandler()`, we'll create a
      * proxy of that component handler just like we did for the plugin object.