Fix Anchor jumping with escaped query components (#14969)

Fix #14968

Signed-off-by: Andrew Thornton <art27@cantab.net>

web_src/js/markdown/anchors.js

@@ -5,7 +5,7 @@ const headingSelector = '.markdown h1, .markdown h2, .markdown h3, .markdown h4,
 function scrollToAnchor() {
   if (document.querySelector(':target')) return;
   if (!window.location.hash || window.location.hash.length <= 1) return;
-  const id = window.location.hash.substring(1);
+  const id = decodeURIComponent(window.location.hash.substring(1));
   const el = document.getElementById(`user-content-${id}`);
   if (el) {
     el.scrollIntoView();