Add to propgrid sample the option to select the way Boolean values are rendered.

This option is useful to demonstrate how to globally change the way Boolean values are rendered (either as check boxes or selection lists).

See #16922.

samples/propgrid/propgrid.h

@@ -186,6 +186,7 @@ public:
     void OnEnableDisable( wxCommandEvent& event );
     void OnSetReadOnly( wxCommandEvent& event );
     void OnHide( wxCommandEvent& event );
+    void OnBoolCheckbox( wxCommandEvent& evt );
     void OnSetBackgroundColour( wxCommandEvent& event );
     void OnClearModifyStatusClick( wxCommandEvent& event );
     void OnFreezeClick( wxCommandEvent& event );