QmlDesigner: Improve resize handle size

The visual representation of the resize handlers was 1 pixel too small
compared to the bounding rects. They were also not centered on the 2px
thick line.

And they simply looked too tiny compared to resize handlers in other
applications.

Change-Id: Idc48d66178cd5f0158efe2f66d685afc4549022e
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

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

@@ -60,7 +60,7 @@ void ResizeHandleItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *
     painter->setPen(pen);
     painter->setRenderHint(QPainter::Antialiasing, false);
     painter->setBrush(QColor(255, 255, 255));
-    painter->drawRect(QRectF(-2., -2., 4., 4.));
+    painter->drawRect(QRectF(-3., -3., 5., 5.));
 
     painter->restore();
 }