Implementing these functions as final does not prevent the object to be
cloned or serialized, so the comment to them was wrong.
However having these functions not public breaks in PHP 8.0.
It still does not make sense to clone or serialise file_system or external_settings classes
but there are a lot of classes in moodle that should not be cloned, no reason to have
a specific solution here.
a7553de7ad