``wcs.high_level_objects_to_values`` and ``wcs.values_to_high_level_objects``
no longer require their ``low_level_wcs`` argument to be a full
``astropy.wcs.wcsapi.BaseLowLevelWCS`` instance. Any object exposing
``world_axis_object_classes`` and ``world_axis_object_components`` attributes
is accepted, and ``serialized_classes`` is now optional (treated as ``False``
if absent).
