feat: first native dialog for modal (#8859)

- The current implementation for modals is provided by fomantic UI.
- This patch introduces a new implementation that relies on the `<dialog>` element to provide modal, whereby the heavy lifting is done by the browser.
- This implementation is considerably simpler, accessible (although untested) and lightweight. It is capable of replacing fomantic UI's modal implementation + our dimmer implementation (~2k lines of code and CSS).[^1] As a first step the empty content modal is migrated.
- This brings in the CSS needed to display `<dialog>` and a helper function that hides some boilerplate code that's needed to show `<dialog>` as a modal.
- Add a E2E test that shows the modal's cancel and approve button works.

[^1]: The heavy work has already been done by me in a local branch, but reviewing that gigantic patch in one PR is not doable.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8859
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

web_src/js/features/repo-editor.js

@@ -6,6 +6,7 @@ import {initMarkupContent} from '../markup/content.js';
 import {attachRefIssueContextPopup} from './contextpopup.js';
 import {POST} from '../modules/fetch.js';
 import {initTab} from '../modules/tab.ts';
+import {showModal} from '../modules/modal.ts';
 
 function initEditPreviewTab($form) {
   const $tabMenu = $form.find('.tabular.menu');
@@ -183,14 +184,8 @@ export function initRepoEditor() {
     commitButton?.addEventListener('click', (e) => {
       // A modal which asks if an empty file should be committed
       if (!$editArea.val()) {
-        $('#edit-empty-content-modal')
-          .modal({
-            onApprove() {
-              document.querySelector('.edit.form').requestSubmit();
-            },
-          })
-          .modal('show');
         e.preventDefault();
+        showModal('edit-empty-content-modal', () => { document.querySelector('.edit.form').requestSubmit()});
       }
     });
   })();