Send wxEVT_DATAVIEW_ITEM_EDITING_DONE after cancelling too

Previously this event was not sent at all if editing the item was
cancelled, e.g. by pressing Esc.

Do send it now from the generic implementation and update the sample to
show this event.

See #17835.

include/wx/dvrenderers.h

@@ -259,6 +259,9 @@ protected:
     wxDataViewCtrl* GetView() const;
 
 private:
+    // Common part of {Cancel,Finish}Editing().
+    bool DoFinishOrCancelEditing(bool cancelled);
+
     // Called from {Called,Finish}Editing() and dtor to cleanup m_editorCtrl
     void DestroyEditControl();