refactor: replace Fomantic modal with native dialog (#39846)

Replace Fomantic's hard-forked jQuery modal with native `<dialog>`
elements, advancing https://github.com/go-gitea/gitea/issues/29849. The
UI is visually unchanged. Dialogs open with `show()` over an `inert`
page, so tooltips, popups and toasts mounted on `<body>` stay usable
above them, unlike with `showModal()`
(https://github.com/whatwg/html/issues/9936).

- Remove the Fomantic modal and dimmer, add `showModal` and `hideModal`
- Declare modals as `<dialog class="modal-dialog">`, shown inside a
`.modal-backdrop`, instead of `ui modal` with its unused size classes
- Remove two modals that could never be opened
- Block the page while a modal is open, close the topmost one on Escape
and restore focus to its opener
- Allow stacked modals, use a confirm modal instead of `window.confirm`
for deleting content history
- Hide popups and toasts when a modal opens or closes
- Keep the release notes modal open when generating notes fails

Fixes: https://github.com/go-gitea/gitea/issues/39643
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/modules/devtest.ts

@@ -1,6 +1,6 @@
 import {showSuccessToast, showInfoToast, showWarningToast, showErrorToast} from './toast.ts';
 import {registerGlobalInitFunc} from './observer.ts';
-import {showFomanticModal} from './fomantic/modal.ts';
+import {showModal} from './modal.ts';
 import {createElementFromHTML} from '../utils/dom.ts';
 import {html} from '../utils/html.ts';
 import {showGlobalErrorMessage} from './errors.ts';
@@ -25,9 +25,9 @@ function initDevtestPage() {
 
   const modalButtons = document.querySelector('.modal-buttons');
   if (modalButtons) {
-    for (const el of document.querySelectorAll('.ui.modal:not([data-skip-button])')) {
+    for (const el of document.querySelectorAll<HTMLDialogElement>('.modal-dialog:not([data-skip-button])')) {
       const btn = createElementFromHTML(html`<button class="ui button">${el.id}</button`);
-      btn.addEventListener('click', () => showFomanticModal(el));
+      btn.addEventListener('click', () => showModal(el));
       modalButtons.append(btn);
     }
   }