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>

templates/projects/list.tmpl

@@ -94,9 +94,9 @@
 </div>
 
 {{if and $.CanWriteProjects (not $.Repository.IsArchived)}}
-<div class="ui small modal" id="repo-project-delete-modal">
+<dialog class="modal-dialog" id="repo-project-delete-modal">
 	<div class="header">{{svg "octicon-trash"}} {{ctx.Locale.Tr "repo.projects.deletion"}}</div>
 	<div class="content"><p>{{ctx.Locale.Tr "repo.projects.deletion_desc"}}</p></div>
 	{{template "base/modal_actions_confirm" .}}
-</div>
+</dialog>
 {{end}}

templates/projects/view.tmpl

@@ -133,7 +133,7 @@
 </div>
 
 {{if $canWriteProject}}
-<div class="ui small modal" id="project-column-modal-edit">
+<dialog class="modal-dialog" id="project-column-modal-edit">
 	<div class="header">{{ctx.Locale.Tr "repo.projects.column.edit"}}</div>
 	<div class="content">
 		<form class="ui form ignore-dirty" method="post" data-action-base-link="{{$.Link}}">
@@ -155,5 +155,5 @@
 			</div>
 		</form>
 	</div>
-</div>
+</dialog>
 {{end}}