Fix Back/Forward menus

We used private API from controls, knowing the risks, and
indeed, the API changed...

Change-Id: Ieb6ae01f4fddbef09240b637012c3b3dfef4b049
Reviewed-by: Andras Becsi <andras.becsi@theqtcompany.com>

tests/quicktestbrowser/ButtonWithMenu.qml

@@ -47,7 +47,7 @@ ToolButton {
     id: root
     property Menu longPressMenu
     function showMenu() {
-        longPressMenu.__popup(0, root.height, 0)
+        longPressMenu.__popup(Qt.rect(0, root.height, 0, 0), 0)
     }
 
     Binding {