Created as a result of the discussion in #1898054-57: Convert comment module to Twig.
There are still two calls to theme() in template_preprocess_comment() that have not been converted to render arrays as part of the Twig conversion. This is because changing them causes test failures, and the concern is that there may be other failures elsewhere that are out of the scope of the Twig conversion process.
This is a separate issue for removing the final uses of theme() in the comment preprocess functions once the conversion has been committed.