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/compose/index.js

@@ -18,6 +18,7 @@ import { mascot } from '../../initial_state';
 import Icon from 'mastodon/components/icon';
 import { logOut } from 'mastodon/utils/log_out';
 import Column from 'mastodon/components/column';
+import { Helmet } from 'react-helmet';
 
 const messages = defineMessages({
   start: { id: 'getting_started.heading', defaultMessage: 'Getting started' },
@@ -145,6 +146,10 @@ class Compose extends React.PureComponent {
       <Column onFocus={this.onFocus}>
         <NavigationContainer onClose={this.onBlur} />
         <ComposeFormContainer />
+
+        <Helmet>
+          <meta name='robots' content='noindex' />
+        </Helmet>
       </Column>
     );
   }