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/controllers/concerns/account_controller_concern.rb

@@ -3,13 +3,12 @@
 module AccountControllerConcern
   extend ActiveSupport::Concern
 
+  include WebAppControllerConcern
   include AccountOwnedConcern
 
   FOLLOW_PER_PAGE = 12
 
   included do
-    layout 'public'
-
     before_action :set_instance_presenter
     before_action :set_link_headers, if: -> { request.format.nil? || request.format == :html }
   end