Forbid jQuery .prop and fix related issues (#29832)

The issue checkbox code received a few more cleanups and I specifically
tested it. The other changes are trivial. Also, I checked the cases for
how many elements match the jQuery selection to determine querySelector
vs. querySelectorAll.

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Co-authored-by: Giteabot <teabot@gitea.io>

web_src/js/features/admin/common.js

@@ -49,7 +49,7 @@ export function initAdminCommon() {
   }
 
   function onUsePagedSearchChange() {
-    if ($('#use_paged_search').prop('checked')) {
+    if (document.getElementById('use_paged_search').checked) {
       showElem('.search-page-size');
       $('.search-page-size').find('input').attr('required', 'required');
     } else {