mediawiki.js: Fix documentation breakage

* Unformatted code and unclosed <media> tag.
  Depending on which versions of other libs are installed, this
  error can occur. Current version (v4.x) in production doesn't
  require this yet. But local environment with the same version
  does. And the next version of jsduck (v5.x) will consistently
  work this way for compliance with Markdown.

* Simplified @link while at it to use the cleaner implied link
  instead like we do elsewhere ({@link} should rarely be
  used directly).

* Add /** @class */ because half the file was no longer indexed
  as part of mw (instead became part of mw.Message after 4f23099)

* Index the private mw#log as log_ instead because it clashes
  with the public mw#log. This should've clashed in 4f23099, but
  didn't because the other one was seen as part of mw.Message
  by the test.

Change-Id: Ic5b8c5c743ecdb1509652c3655d83e501f6fa9ee
(cherry picked from commit 176e3e44a01dc5d5b020f276649123d743458d8f)