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

app/serializers/rest/search_serializer.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class REST::SearchSerializer < ActiveModel::Serializer
+  attributes :hashtags
+
+  has_many :accounts, serializer: REST::AccountSerializer
+  has_many :statuses, serializer: REST::StatusSerializer
+
+  def hashtags
+    object.hashtags.map(&:name)
+  end
+end