Render htmlentities correctly for links not supported by Rinku

Closes #41719

See merge request gitlab-org/gitlab-ce!17180

Rinku 2.0.0 (the version we use) will remove the last character of a link if
it's a closing part of a punctuation pair (different types of parentheses and
quotes), unless both of the below are true:

1. The matching pair has different start and end characters.
2. There are equal numbers of both in the matched string (they don't have to be
   balanced).

Since the redactor can be run on multiple documents at once and
query results are stored in the request store.

[10.4] Fix stored XSS in code blocks