This commit allows Action Text to be used without having an
ApplicationController defined. In doing so, it also fixes Action Text
attachments to render the correct URL host in mailers.
It also avoids allocating an ActionController::Renderer per request.
Fixes#37183.
Fixes#35578.
Fixes#36963.
Closes#38714.
Co-authored-by: Jeremy Daer <jeremydaer@gmail.com>
