Make ext.uls.mediawiki depend upon ext.uls.init

With the user preference now enabled, we can no longer
assume that ext.uls.init will be loaded on every view.

This also fixes integration with the Translate extension.

Bug: 46306
Change-Id: I05c76e478ddcfb29000471dc79ca35ce77ad59b8
(cherry picked from commit 7071db6ede1f062f1cda1eb5689ec16271d2a337)