QLegendData: Properly expose it to QML

Also, fix the docs to correctly mark it as a value type.

Pick-to: 6.10
Change-Id: I68405ba4b0c32b0d9c84b0913031e5e124de1bc0
Reviewed-by: Sami Varanka <sami.varanka@qt.io>
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/graphs2d/qabstractseries.cpp

@@ -42,15 +42,18 @@ QT_BEGIN_NAMESPACE
 */
 
 /*!
-    \qmltype LegendData
+    \qmlvaluetype legendData
     \nativetype QLegendData
     \inqmlmodule QtGraphs
     \ingroup graphs_qml__2D
-    \brief The LegendData struct contains information to display on a sets
+    \brief The legendData value type contains information to display on a sets
     legend marker.
 
     The information needed to make a visual association between a set and a
     marker include properties such as color, border color, and a name of a set.
+
+    \note Before Qt 6.10, this value type was only provided as an anonymous
+    type.
 */
 
 /*!

src/graphs2d/qabstractseries.h

@@ -19,6 +19,8 @@ class QGraphsView;
 struct Q_GRAPHS_EXPORT QLegendData
 {
     Q_GADGET
+    QML_VALUE_TYPE(legendData)
+    QML_ADDED_IN_VERSION(6, 10) // formerly anonymous
     Q_PROPERTY(QColor color MEMBER color FINAL)
     Q_PROPERTY(QColor borderColor MEMBER borderColor FINAL)
     Q_PROPERTY(QString label MEMBER label FINAL)