Improve the loading time of ULS language selector by fetching modules early

Start fetching them on mouseover without waiting for click.

Bug: T299202
Change-Id: I1ba3b8516bd01ad1bf8bb4c57d72d10ca59e06ca

resources/js/ext.uls.interface.js

@@ -378,6 +378,10 @@
 		}
 
 		$trigger.on( 'click', clickHandler );
+		// Optimization: Prefetch the Resource loader modules for ULS on mouseover
+		$trigger.one( 'mouseover', function () {
+			mw.loader.load( languageSettingsModules );
+		} );
 	}
 
 	function initLanguageChangeUndoTooltip() {