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/common-global.js

@@ -8,6 +8,7 @@ import {attachCheckboxAria, attachDropdownAria} from './aria.js';
 import {handleGlobalEnterQuickSubmit} from './comp/QuickSubmit.js';
 import {initTooltip} from '../modules/tippy.js';
 import {svg} from '../svg.js';
+import {hideElem, showElem, toggleElem} from '../utils/dom.js';
 
 const {appUrl, csrfToken} = window.config;
 
@@ -118,7 +119,7 @@ export function initGlobalCommon() {
   $('.tabable.menu .item').tab();
 
   $('.toggle.button').on('click', function () {
-    $($(this).data('target')).slideToggle(100);
+    toggleElem($($(this).data('target')));
   });
 
   // make table <tr> and <td> elements clickable like a link
@@ -317,7 +318,7 @@ export function initGlobalLinkActions() {
 
 export function initGlobalButtons() {
   $('.show-panel.button').on('click', function () {
-    $($(this).data('panel')).show();
+    showElem($(this).data('panel'));
   });
 
   $('.hide-panel.button').on('click', function (event) {
@@ -325,12 +326,12 @@ export function initGlobalButtons() {
     event.preventDefault();
     let sel = $(this).attr('data-panel');
     if (sel) {
-      $(sel).hide();
+      hideElem($(sel));
       return;
     }
     sel = $(this).attr('data-panel-closest');
     if (sel) {
-      $(this).closest(sel).hide();
+      hideElem($(this).closest(sel));
       return;
     }
     // should never happen, otherwise there is a bug in code