Add \since 6.0 to new function

Also fix general style of the documentation.

Task-number: QTBUG-86479
Change-Id: Ia46bb3ec02d6474dd79b8ac733e0c613abc5e0d8
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

src/widgets/graphicsview/qgraphicslayoutitem.cpp

@@ -827,12 +827,16 @@ void QGraphicsLayoutItem::updateGeometry()
 }
 
 /*!
- * returns \c true if this item is empty, i.e whether it has no content and
- * should not occupy any space.
- *
- * The default implementation returns true if the item has been hidden unless
- * its size policy has retainSizeWhenHidden set to \c true
- */
+    \since 6.0
+
+    Returns \c true if this item is empty, i.e whether it has no content and
+    should not occupy any space.
+
+    The default implementation returns \c true true if the item has been hidden,
+    unless its \l{sizePolicy()}{size policy} has retainSizeWhenHidden set to \c true
+
+    \sa sizePolicy()
+*/
 bool QGraphicsLayoutItem::isEmpty() const
 {
     bool isHidden = false;