Use Codex styles for buttons in language overlay (attempt 2)

* Replace all instances of mw-ui markup with Codex markup
* Use codex-search-styles
* Where codex-search-styles is not installed (e.g. 1.39)
register an alias which points to @wikimedia/codex as that is
available.

Bug: T340255
Bug: T340257
Change-Id: I4f3ddfb68ea6c033ee7a49729187f4ddbc8abe5c

resources/js/ext.uls.setlang.js

@@ -42,11 +42,11 @@
 
 	function getButtons() {
 		$cancelBtn = $( '<button>' )
-			.addClass( 'mw-ui-button uls-setlang-cancel' )
+			.addClass( 'cdx-button uls-setlang-cancel' )
 			.text( mw.msg( 'ext-uls-setlang-cancel' ) );
 
 		$acceptBtn = $( '<button>' )
-			.addClass( 'mw-ui-button mw-ui-progressive active uls-setlang-apply' )
+			.addClass( 'cdx-button cdx-button--type-primary cdx-button--action-progressive active uls-setlang-apply' )
 			.text( mw.msg( 'ext-uls-setlang-accept' ) );
 
 		return $( '<div>' )