gtk_scale_set_format_value_func() has no GDestroyNotify parameter
The new (in gtk4) function gtk_scale_set_format_value_func()
has no GDestroyNotify destroy
parameter. It would be useful, at least in gtkmm, where gpointer user_data
would
be a pointer to a data structure that should be deleted when it's no longer needed.
Compare gtk_drawing_area_set_draw_func()
and several other functions.