import-checker: allow all absolute imports of stdlib modules
Before this patch, we didn't allow imports like
from importlib import resources
(That's the reason I used `import importlib.resources` in D7629.)
I think that form is still an absolute import, so I don't think we
forbade on purpose.
Differential Revision: https://phab.mercurial-scm.org/D7700
#require docutils gettext
$ $TESTDIR/check-gendoc el
checking for parse errors