Set hreflang attribute to the links

They are present in the original links in the skin, so copy them to ULS too.

Bug: T327591
Change-Id: I24566d1ff4c8c655325ec0dc601f56d73e414d5f

resources/js/ext.uls.launch.js

@@ -121,7 +121,8 @@ function launchULS( $trigger, languagesObject, forCLS ) {
 			$languageLink
 				.prop( {
 					href: element.href,
-					title: element.title
+					title: element.title,
+					hreflang: element.hreflang
 				} )
 				.text( element.textContent );