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/fetch-action.ts

@@ -231,10 +231,10 @@ export async function submitFormFetchAction(elForm: HTMLFormElement, opts: Submi
 }
 
 async function confirmFetchAction(el: HTMLElement) {
-  let elModal: HTMLElement | null = null;
+  let elModal: HTMLDialogElement | null = null;
   const dataModalConfirm = el.getAttribute('data-modal-confirm') || '';
   if (dataModalConfirm.startsWith('#') && dataModalConfirm.length > 1) {
-    elModal = document.querySelector<HTMLElement>(`#${CSS.escape(dataModalConfirm.substring(1))}`);
+    elModal = document.querySelector<HTMLDialogElement>(`#${CSS.escape(dataModalConfirm.substring(1))}`);
     if (elModal) {
       elModal = createElementFromHTML(elModal.outerHTML);
       elModal.removeAttribute('id');