The down appearance (`D`) is optional and not available in the document
from #12233, so the checkboxes are never saved/printed as checked
because the checked appearance is based on the export value that is
missing because the `D` entry is not available.
Instead, we should use the normal appearance (`N`) since that one is
required and therefore always available.
Finally, the /Off appearance is optional according to section 12.7.4.2.3
of the specification, so that needs to be taken into account to match
the specification and to fix reference test failures for the
`annotation-button-widget-print` test. That is a file that doesn't
specify an /Off appearance in the normal appearance dictionary.
a8efc0296b