Allow GUIs to optionally update on a timer

Otherwise plugins can't update their editors when the GUI is being blocked.

src/wine-host/editor.h

@@ -32,8 +32,11 @@ class Editor {
     /**
      * Open a window and return a handle to the new Win32 window that can be
      * used by the hosted VST plugin.
+     *
+     * @param effect The plugin this window is being created for. Used to send
+     *   `effEditIdle` messages on a timer.
      */
-    HWND open();
+    HWND open(AEffect* effect);
     void close();
 
     /**
@@ -64,6 +67,9 @@ class Editor {
      */
     bool embed_into(const size_t parent_window_handle);
 
+    // Needed to handle idle updates through a timer
+    AEffect* plugin;
+
    private:
     /**
      * Return the X11 window handle for the window if it's currently open.