Fix using radio buttons in wxDataViewToggleRenderer under macOS

Changing item cell in ShowAsRadio() was wrong as the item cell doesn't
exist when it is called and changing the column cell didn't seem to work
well, so just recreate the entire cell in it instead.

See https://github.com/wxWidgets/wxWidgets/pull/853

include/wx/osx/dvrenderers.h

@@ -207,6 +207,8 @@ public:
                                   unsigned col);
 
 private:
+    void DoInitButtonCell(int buttonType);
+
     wxDECLARE_DYNAMIC_CLASS_NO_COPY(wxDataViewToggleRenderer);
 };