Export QQuickItemViewFxItem privately

We need it for release builds of the new TreeView
(for most subclasses of QQuickTableViewPrivate actually).

Task-number: QTBUG-61630
Change-Id: I35c52ef1336ecc2cdfafa8fba473890ce2cff2ba
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/quick/items/qquickitemviewfxitem_p_p.h

@@ -60,7 +60,7 @@ QT_REQUIRE_CONFIG(quick_itemview);
 
 QT_BEGIN_NAMESPACE
 
-class Q_AUTOTEST_EXPORT QQuickItemViewFxItem
+class Q_QUICK_PRIVATE_EXPORT QQuickItemViewFxItem
 {
 public:
     QQuickItemViewFxItem(QQuickItem *item, bool ownItem, QQuickItemChangeListener *changeListener);