WebUI: Replace getElements & getChildren

This PR further reduces Mootools usage.
PR #22220.

src/webui/www/private/scripts/search.js

@@ -166,7 +166,7 @@ window.qBittorrent.Search ??= (() => {
     };
 
     const numSearchTabs = () => {
-        return $("searchTabs").getElements("li").length;
+        return document.querySelectorAll("#searchTabs li").length;
     };
 
     const getSearchIdFromTab = (tab) => {