Don't load mediawiki.ui.button on page load

The stylesheet is needed on legacy Vector but not modern
Vector 2022 meaning Vector 2022 loads two sets of styles
for buttons.

This is a short term fix until UniversalLanguageSelector can
use Codex.

Bug: T340255
Change-Id: Ib4e228908d2813898654886bc1ee76e90dc52f22

extension.json

@@ -157,6 +157,7 @@
 				"vector-2022": "css/ext.uls-vector.less"
 			},
 			"dependencies": [
+				"mediawiki.ui.button",
 				"jquery.uls.data",
 				"mediawiki.api",
 				"mediawiki.cookie",
@@ -172,8 +173,7 @@
 			"dependencies": [
 				"mediawiki.jqueryMsg",
 				"mediawiki.language",
-				"ext.uls.common",
-				"mediawiki.ui.button"
+				"ext.uls.common"
 			],
 			"messages": [
 				"ext-uls-compact-link-count",

resources/js/ext.uls.compactlinks.js

@@ -190,7 +190,9 @@
 			this.compactList[ language ].parentNode.style.display = '';
 		}
 
+		mw.loader.using( 'mediawiki.ui.button' ).then( function () {
 			this.addTrigger();
+		} );
 
 		mw.hook( 'mw.uls.compactlinks.initialized' ).fire( true );
 	};