Following on from I6fa966c2, fire the mw.uls.compact_language_links.open hook with the $trigger parameter as context for clients to be able to able to distinguish which treatment is visible to the user. Supporting changes: - Note that the hook is unstable next to its callsite Bug: T280770 Change-Id: Ie4bbfea4dc5e36401df587550f466aeae5c8fdcc