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/admin/user/edit.tmpl

@@ -223,7 +223,7 @@
 		</div>
 	</div>
 
-<div class="ui g-modal-confirm delete modal" id="delete-user-modal">
+<dialog class="modal-dialog" id="delete-user-modal">
 	<div class="header">
 		{{svg "octicon-trash"}}
 		{{ctx.Locale.Tr "settings.delete_account_title"}}
@@ -241,6 +241,6 @@
 		</div>
 		{{template "base/modal_actions_confirm" .}}
 	</form>
-</div>
+</dialog>
 
 {{template "admin/layout_footer" .}}

templates/admin/user/view_orgs.tmpl

@@ -5,18 +5,20 @@
 	<span>{{ctx.Locale.Tr "settings.organization"}} ({{ctx.Locale.Tr "admin.total" $userOrgsTotal}})</span>
 	{{if $userOrgs}}
 		<button type="button" class="ui red tiny button show-modal" data-modal="#remove-all-orgs-modal">{{ctx.Locale.Tr "remove_all"}}</button>
-		<form class="ui small modal form-fetch-action" id="remove-all-orgs-modal" method="post" action="{{ctx.RootData.Link}}/orgs/remove-all">
+		<dialog class="modal-dialog" id="remove-all-orgs-modal">
 			<div class="header">
 				{{ctx.Locale.Tr "admin.users.remove_all_orgs_title"}}
 			</div>
-			<div class="content">
-				<p>{{ctx.Locale.Tr "admin.users.remove_all_orgs_desc" $user.Name $userOrgsTotal}}</p>
-			</div>
-			<div class="actions">
-				<div class="ui cancel button">{{ctx.Locale.Tr "settings.cancel"}}</div>
-				<button class="ui red button" type="submit">{{ctx.Locale.Tr "remove_all"}}</button>
-			</div>
-		</form>
+			<form class="form-fetch-action" method="post" action="{{ctx.RootData.Link}}/orgs/remove-all">
+				<div class="content">
+					<p>{{ctx.Locale.Tr "admin.users.remove_all_orgs_desc" $user.Name $userOrgsTotal}}</p>
+				</div>
+				<div class="actions">
+					<div class="ui cancel button">{{ctx.Locale.Tr "settings.cancel"}}</div>
+					<button class="ui red button" type="submit">{{ctx.Locale.Tr "remove_all"}}</button>
+				</div>
+			</form>
+		</dialog>
 	{{end}}
 </h4>