Support rich references in links (!7951) · Merge requests · GitLab.org / GitLab FOSS · GitLab

Continuation of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7313.

Still to do:

Handle characters which can appear in titles but not element content, and vice versa: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7313#note_18456852
Make sure post-processing filters are defined in one place: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7313#note_18786344
Handle verbosity levels in Referable: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7313#note_18460145
Allow non-link-text expansions: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7313#note_18792208

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/23177.