Add status references support

app/serializers/rest/status_serializer.rb

@@ -6,6 +6,7 @@ class REST::StatusSerializer < ActiveModel::Serializer
   attributes :id, :created_at, :in_reply_to_id, :in_reply_to_account_id,
              :sensitive, :spoiler_text, :visibility, :visibility_ex, :language,
              :uri, :url, :replies_count, :reblogs_count, :searchability, :markdown,
+             :status_reference_ids, :status_references_count, :status_referred_by_count,
              :favourites_count, :emoji_reactions, :emoji_reactions_count, :reactions, :edited_at
 
   attribute :favourited, if: :current_user?
@@ -92,6 +93,14 @@ class REST::StatusSerializer < ActiveModel::Serializer
     ActivityPub::TagManager.instance.url_for(object)
   end
 
+  def status_reference_ids
+    @status_reference_ids = object.reference_objects.pluck(:target_status_id)
+  end
+
+  def status_references_count
+    status_reference_ids.size
+  end
+
   def favourited
     if instance_options && instance_options[:relationships]
       instance_options[:relationships].favourites_map[object.id] || false