Refactor formatter (#17828)

* Refactor formatter

* Move custom emoji pre-rendering logic to view helpers

* Move more methods out of Formatter

* Fix code style issues

* Remove Formatter

* Add inline poll options to RSS feeds

* Remove unused helper method

* Fix code style issues

* Various fixes and improvements

* Fix test

app/serializers/rest/announcement_serializer.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class REST::AnnouncementSerializer < ActiveModel::Serializer
+  include FormattingHelper
+
   attributes :id, :content, :starts_at, :ends_at, :all_day,
              :published_at, :updated_at
 
@@ -25,7 +27,7 @@ class REST::AnnouncementSerializer < ActiveModel::Serializer
   end
 
   def content
-    Formatter.instance.linkify(object.text)
+    linkify(object.text)
   end
 
   def reactions