WebUI: Replace Mootools class list manipulation methods

All `addClass()`, `removeClass()` and `hasClass()` instances were changed to use `classList` equivalent:
https://developer.mozilla.org/en-US/docs/Web/API/Element/classList

PR #21946.

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Co-authored-by: Chocobo1 <Chocobo1@users.noreply.github.com>

src/webui/www/private/scripts/prop-trackers.js

@@ -43,8 +43,8 @@ window.qBittorrent.PropTrackers ??= (() => {
     let loadTrackersDataTimer = -1;
 
     const loadTrackersData = () => {
-        if ($("propTrackers").hasClass("invisible")
-            || $("propertiesPanel_collapseToggle").hasClass("panel-expand")) {
+        if ($("propTrackers").classList.contains("invisible")
+            || $("propertiesPanel_collapseToggle").classList.contains("panel-expand")) {
             // Tab changed, don't do anything
             return;
         }