The `mediawiki.skinning.interface` module includes the `toc` feature
which is enabled by default,
which requires a working localization environment which requires
DBLoadBalancer which is disabled at this entry point.
Instead use ResourceLoaderSkinModule directly with an opt-in
policy where toc feature is not disbled.
This means the definition in Resources.php is no longer
necessary so it is marked for deprecation. The installer
now works.
A unit test is added to make sure the installer stylesheet
doesn't break again.
Bug: T270027
Change-Id: I851fcd0e50e3a70158d5bfa1fdcae3cd278694d6
