Convert internal node/123 style paths to pretty path aliases for links within content in modern Drupal 8 9

The evidence that LinkIt does support was in https://www.drupal.org/project/linkit/issues/2988145, and then we found it also did it as a filter, the good old style, which i was happy to see, but apparently the filter is LinkIt-specific.

This module, the usual go-to in Drupal 7, looks like it’s been upgraded to Drupal 8 and even has Drupal 9 fixes awaiting review, but no one has cut a release: https://www.drupal.org/project/intlinks

Pathologic should also be an option.

See also: 2019-09-29-providing-a-recommended-citation-format-for-content-on-your-website.md