Move skeleton methods from AV to AbsC

The methods:

 * #render_to_body
 * #render_to_string
 * #_normalize_render

Haven't had anything specyfic to ActionView. This was common code which should belong to AbstractController
Make Mime::TEXT default format in AbstractController
Move BasicRendering to AbstractController
Merge pull request #12121 from strzalek/move-methods-to-abs-controller

Move glue methods & BasicRendering to AbstractController