Refactor hiding-methods, remove jQuery show/hide, remove .hide class, remove inline style=display:none (#22950)

Close #22847

This PR:

* introduce Gitea's own `showElem` and related functions
* remove jQuery show/hide
* remove .hide class
* remove inline style=display:none 

From now on:

do not use:
* "[hidden]" attribute: it's too weak, can not be applied to an element
with "display: flex"
* ".hidden" class: it has been polluted by Fomantic UI in many cases
* inline style="display: none": it's difficult to tweak
* jQuery's show/hide/toggle: it can not show/hide elements with
"display: xxx !important"

only use:
* this ".gt-hidden" class
* showElem/hideElem/toggleElem functions in "utils/dom.js"

cc: @silverwind , this is the all-in-one PR

web_src/js/features/repo-template.js

@@ -1,5 +1,6 @@
 import $ from 'jquery';
 import {htmlEscape} from 'escape-goat';
+import {hideElem, showElem} from '../utils/dom.js';
 
 const {appSubUrl} = window.config;
 
@@ -9,11 +10,11 @@ export function initRepoTemplateSearch() {
     const $templateUnits = $('#template_units');
     const $nonTemplate = $('#non_template');
     if ($repoTemplate.val() !== '' && $repoTemplate.val() !== '0') {
-      $templateUnits.show();
-      $nonTemplate.hide();
+      showElem($templateUnits);
+      hideElem($nonTemplate);
     } else {
-      $templateUnits.hide();
-      $nonTemplate.show();
+      hideElem($templateUnits);
+      showElem($nonTemplate);
     }
   };
   $repoTemplate.on('change', checkTemplate);