Don't link wikilinks in section heading autocomments

Don't link wikilinks in section heading autocomments

Previously, a manually constructed autocomment in the form of
/* [[Some link]] */

would create a link to the the section, and then the "Some link" page.

After T165189 was implemented, the entire autocomment is now a link to
the section, so we're creating links inside of a link...which is
problematic. In most contexts (history and watchlist particularly), the
section link is more important than the title in the section heading, so
that's what we'll favor here.

It's worth noting that this situation is a manually created edge case.
Even if the section heading is a wikilink, the edit summary will
autofill a section autocomment without the double brackets.

We'll now render the double brackets ([[...]]) and not link them. This
is what the user literally typed, and matches the existing practice of
rendering templates in section headings with their literal syntax. And
as a bonus, it's still possible for user scripts such as wikEdDiff to
turn the rendered double brackets into a real link if users want.

Bug: T165189
Change-Id: Ib10679edd76c72a60d7e1c89fc8454166e34c463