QmlDesigner: Adjust margings for "move zone"

I introduced a zone around the boarder of each item where
it can always be dragged,
instead of selection another overlapping item.
The area is now a lot smaller, but the 4px seem enough for me
when testing it.
This zone is slightly to big. I keep the size of 20px at the top
so the label/gizmo is always dragable.

Change-Id: Ia1b8afb822b506f5322b952d5537eafc73b52ea2
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

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

@@ -152,8 +152,8 @@ bool AbstractFormEditorTool::selectedItemCursorInMovableArea(const QPointF &pos)
     QRectF boundingRect = boundingRectInSceneSpace.boundingRect();
     QRectF innerRect = boundingRect;
 
-    innerRect.adjust(10, 10, -10, -10);
-    boundingRect.adjust(-10, -20, 10, 10);
+    innerRect.adjust(2, 2, -2, -2);
+    boundingRect.adjust(-2, -20, 2, 2);
 
     return !innerRect.contains(pos) && boundingRect.contains(pos);
 }