Fire language change hook

As of Id345e933, we fire the language change hook when the user switches
language by clicking on a link in the languages list. In order to
compare the user switching language in the scenario above with the user
switching language via the CLS and/or Vector's language switcher, ensure
that we fire language change hook in all treatments.

Bug: T280770
Change-Id: I4a74254612557c287b16f4f086077a2637de9a2e

resources/js/ext.uls.launch.js

@@ -60,6 +60,9 @@ function launchULS( $trigger, languagesObject, forCLS ) {
 			) {
 				return;
 			}
+
+			mw.hook( 'mw.uls.interface.language.change' ).fire( language );
+
 			location.href = languagesObject[ language ].href;
 		},
 		onPosition: function () {