AudioApplet: Fix applet positioning bug

Currently when clicking the percentage toggle, there is a delay
in moving the applet window position. This is because after
the applet is resized, the applet area is repositioned
asynchronously. This takes advantage of the new AppletAreaRectChange
event to reposition the slider window when necessary.

Userland/Applets/Audio/main.cpp

@@ -81,7 +81,6 @@ public:
                 window()->resize(44, 16);
                 m_percent_box->set_tooltip("Hide percent");
             }
-            reposition_slider_window();
             GUI::Application::the()->hide_tooltip();
 
             Config::write_bool("AudioApplet", "Applet", "ShowPercent", m_show_percent);
@@ -152,6 +151,11 @@ private:
         }
     }
 
+    virtual void applet_area_rect_change_event(GUI::AppletAreaRectChangeEvent&) override
+    {
+        reposition_slider_window();
+    }
+
     void open()
     {
         reposition_slider_window();