In RimProject, encode/decode into a string the currentIndex from QTreeView.

This will also make sure the active view is restored when opening a project
p4#: 21463

ApplicationCode/ProjectDataModel/RimUiTreeView.h

@@ -46,6 +46,9 @@ public:
     void applyTreeViewStateFromString(const QString& treeViewState);
     void storeTreeViewStateToString(QString& treeViewState);
 
+    static void applyCurrentIndexFromString(QAbstractItemView& itemView, const QString& currentIndexString);
+    static void storeCurrentIndexToString(const QAbstractItemView& itemView, QString& currentIndexString);
+
 protected:
     void contextMenuEvent(QContextMenuEvent* event);