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/lib/plain_text_formatter.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class PlainTextFormatter
+  include ActionView::Helpers::TextHelper
+
+  NEWLINE_TAGS_RE = /(<br \/>|<br>|<\/p>)+/.freeze
+
+  attr_reader :text, :local
+
+  alias local? local
+
+  def initialize(text, local)
+    @text  = text
+    @local = local
+  end
+
+  def to_s
+    if local?
+      text
+    else
+      strip_tags(insert_newlines).chomp
+    end
+  end
+
+  private
+
+  def insert_newlines
+    text.gsub(NEWLINE_TAGS_RE) { |match| "#{match}\n" }
+  end
+end