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-common.js

@@ -1,4 +1,5 @@
 import $ from 'jquery';
+import {hideElem, showElem, toggleElem} from '../utils/dom.js';
 
 const {csrfToken} = window.config;
 
@@ -76,8 +77,8 @@ export function initRepoCommonBranchOrTagDropdown(selector) {
   $(selector).each(function () {
     const $dropdown = $(this);
     $dropdown.find('.reference.column').on('click', function () {
-      $dropdown.find('.scrolling.reference-list-menu').hide();
-      $($(this).data('target')).show();
+      hideElem($dropdown.find('.scrolling.reference-list-menu'));
+      showElem($($(this).data('target')));
       return false;
     });
   });
@@ -102,7 +103,7 @@ export function initRepoCommonLanguageStats() {
   if ($('.language-stats').length > 0) {
     $('.language-stats').on('click', (e) => {
       e.preventDefault();
-      $('.language-stats-details, .repository-menu').slideToggle();
+      toggleElem($('.language-stats-details, .repository-menu'));
     });
   }
 }