Show drop menu at correct global position

The coordinates we get are relative to the containment.
Before when dragging a file to a second screen it would show the menu
on the first screen.

src/scriptengines/qml/plasmoid/containmentinterface.cpp

@@ -428,7 +428,7 @@ void ContainmentInterface::processMimeData(QMimeData *mimeData, int x, int y, KI
         }
         return;
     }
-    m_dropMenu = QPointer<DropMenu>(new DropMenu(dropJob, QPoint(x, y), this));
+    m_dropMenu = QPointer<DropMenu>(new DropMenu(dropJob, mapToGlobal(QPoint(x, y)).toPoint(), this));
     if (dropJob) {
         dropJob->setParent(m_dropMenu);
     }