Add action=query&meta=languageinfo API module

Add action=query&meta=languageinfo API module

This API module can be used to get information about all the languages
supported by this MediaWiki installation. Since parts of this
information, such as the fallback chain, are expensive to retrieve if
the localization cache is not populated, we apply continuation if the
request is taking too long (suggested by Anomie in T217239#4994301); we
don’t expect this to happen in Wikimedia production, though.

Bug: T74153
Bug: T220415
Change-Id: Ic66991cd85ed4439a47bfb1412dbe24c23bd9819