QmlDesigner: Fix magic move offset

There is a magic offset that increases the move tool hitbox.
We should take the zoom factor into account.

Change-Id: Ib2ebb310100aa9e5ba5102e9b44d4a38f6187ced
Reviewed-by: Aleksei German <aleksei.german@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmldesigner/components/formeditor/abstractformeditortool.cpp

@@ -149,7 +149,8 @@ bool AbstractFormEditorTool::selectedItemCursorInMovableArea(const QPointF &pos)
     QRectF innerRect = boundingRect;
 
     innerRect.adjust(2, 2, -2, -2);
-    boundingRect.adjust(-2, -20, 2, 2);
+    const int heightOffset = -20 / scene()->formLayerItem()->viewportTransform().m11();
+    boundingRect.adjust(-2, heightOffset, 2, 2);
 
     return !innerRect.contains(pos) && boundingRect.contains(pos);
 }