Refactor JSON templates to be generated with ActiveModelSerializers instead of Rabl (#4090)

app/serializers/rest/media_attachment_serializer.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class REST::MediaAttachmentSerializer < ActiveModel::Serializer
+  include RoutingHelper
+
+  attributes :id, :type, :url, :preview_url,
+             :remote_url, :text_url, :meta
+
+  def url
+    full_asset_url(object.file.url(:original))
+  end
+
+  def preview_url
+    full_asset_url(object.file.url(:small))
+  end
+
+  def text_url
+    medium_url(object.id)
+  end
+
+  def meta
+    object.file.meta
+  end
+end