Menu: Create visual menu items lazily

Change-Id: I68c21248f7779002275815d339a0e982ed6f2860
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>

src/qtdesktop/Menu.qml

@@ -138,6 +138,12 @@ MenuPrivate {
 
     //! internal
     menuContentItem: Loader {
+        sourceComponent: menuComponent
+        active: !root.isNative && root.popupVisible
+        focus: true
+    }
+
+    property Component menuComponent: Loader {
         id: menuFrameLoader
 
         property var menu: root
@@ -147,7 +153,6 @@ MenuPrivate {
         property int itemWidth: item ? item.implicitWidth : 0
 
         visible: menu.popupVisible && status === Loader.Ready
-        active: !menu.isNative && menu.popupVisible
         sourceComponent: menuFrameStyle
 
         focus: true