Refactor some frontend problems (#32646)

1. correct the modal usage on "admin email list" page (then
`web_src/js/features/admin/emails.ts` is removed)
2. use `addDelegatedEventListener` instead of `jQuery().on`
3. more jQuery related changes and remove jQuery from
`web_src/js/features/common-button.ts`
4. improve `confirmModal` to make it support header, and remove
incorrect double-escaping
5. fix more typescript related types
6. fine tune devtest pages and add more tests

templates/devtest/flex-list.tmpl

@@ -1,5 +1,4 @@
-{{template "base/head" .}}
-<link rel="stylesheet" href="{{AssetUrlPrefix}}/css/devtest.css?v={{AssetVersion}}">
+{{template "devtest/devtest-header"}}
 <div class="page-content devtest">
 	<div class="ui container">
 		<h1>Flex List (standalone)</h1>
@@ -112,4 +111,4 @@
 		</div>
 	</div>
 </div>
-{{template "base/footer" .}}
+{{template "devtest/devtest-footer"}}