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/serializers/rest/account_serializer.rb

@@ -14,6 +14,7 @@ class REST::AccountSerializer < ActiveModel::Serializer
 
   attribute :suspended, if: :suspended?
   attribute :silenced, key: :limited, if: :silenced?
+  attribute :noindex, if: :local?
 
   class FieldSerializer < ActiveModel::Serializer
     include FormattingHelper
@@ -103,7 +104,11 @@ class REST::AccountSerializer < ActiveModel::Serializer
     object.silenced?
   end
 
-  delegate :suspended?, :silenced?, to: :object
+  def noindex
+    object.user_prefers_noindex?
+  end
+
+  delegate :suspended?, :silenced?, :local?, to: :object
 
   def moved_and_not_nested?
     object.moved? && object.moved_to_account.moved_to_account_id.nil?