Add strike-through support to wxDataViewItem attributes

Implement support for this attribute only in the generic version so far,
it will hopefully be implemented for the natives ones in the future.

Also add a new toggle column to the dataview sample to check how it
works: checking the items in this column enables using this attribute
for some other ones.

Closes #18180.

samples/dataview/dataview.cpp

@@ -725,6 +725,11 @@ void MyFrame::BuildDataViewCtrl(wxPanel* parent, unsigned int nPanel, unsigned l
             m_list_model = new MyListModel;
             m_ctrl[1]->AssociateModel( m_list_model.get() );
 
+            m_ctrl[1]->AppendToggleColumn(L"\u2714",
+                                          MyListModel::Col_Toggle,
+                                          wxDATAVIEW_CELL_ACTIVATABLE,
+                                          wxCOL_WIDTH_AUTOSIZE);
+
             // the various columns
             m_ctrl[1]->AppendTextColumn("editable string",
                                         MyListModel::Col_EditableText,