Althrougth the MenuBar in QtWidgets module works with KDE's global appmenu, but MenuBar in QtQuick.Controls2 does not, it will always stays in the app's frame, never shown in the KDE's global appmenu!

Reproduce steps:

1. add an applicatin menu panel in the plasma desktop
2. create a quick app in the qtcreator
3. modify the Main.qml, make it as the following:

   import QtQuick
   import QtQuick.ControlsApplicationWindow {
       width: 640
       height: 480
       visible: true
       title: qsTr("Hello World")
       menuBar: MenuBar {
           Menu {
               id: menu
               title: "AA"
               MenuItem {
                   text: "BBB"
               }
           }
           Menu {
               title: "BB"
               MenuItem {
                   text: "BBB"
               }
           }
           Menu {
               title: "CC"
               MenuItem {
                   text: "BBB"
               }
           }
       }
   } 

   4. Run it