Change public accounts pages to mount the web UI (#19319)

* Change public accounts pages to mount the web UI

* Fix handling of remote usernames in routes

- When logged in, serve web app
- When logged out, redirect to permalink
- Fix `app-body` class not being set sometimes due to name conflict

* Fix missing `multiColumn` prop

* Fix failing test

* Use `discoverable` attribute to control indexing directives

* Fix `<ColumnLoading />` not using `multiColumn`

* Add `noindex` to accounts in REST API

* Change noindex directive to not be rendered by default before a route is mounted

* Add loading indicator for detailed status in web UI

* Fix missing indicator appearing while account is loading in web UI

app/javascript/mastodon/features/follow_recommendations/index.js

@@ -12,6 +12,7 @@ import Column from 'mastodon/features/ui/components/column';
 import Account from './components/account';
 import imageGreeting from 'mastodon/../images/elephant_ui_greeting.svg';
 import Button from 'mastodon/components/button';
+import { Helmet } from 'react-helmet';
 
 const mapStateToProps = state => ({
   suggestions: state.getIn(['suggestions', 'items']),
@@ -104,6 +105,10 @@ class FollowRecommendations extends ImmutablePureComponent {
             </React.Fragment>
           )}
         </div>
+
+        <Helmet>
+          <meta name='robots' content='noindex' />
+        </Helmet>
       </Column>
     );
   }