Add a test for selecting the last item in the tree control sample.

This allows to test whether an item is brought into view by selecting it,
see #11154.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64650 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/treectrl/treetest.h

@@ -272,6 +272,7 @@ public:
         { DoShowRelativeItem(&wxTreeCtrl::GetNextSibling, "next sibling"); }
 
     void OnScrollTo(wxCommandEvent& event);
+    void OnSelectLast(wxCommandEvent& event);
 
     void OnIdle(wxIdleEvent& event);
     void OnSize(wxSizeEvent& event);
@@ -368,5 +369,6 @@ enum
     TreeTest_ShowPrevSibling,
     TreeTest_ShowNextSibling,
     TreeTest_ScrollTo,
+    TreeTest_SelectLast,
     TreeTest_Ctrl = 1000
 };