Create a trait to add in the renderer service

drupal_render() and drupal_render_root() are deprecated global functions. Classes often have to wrap these functions, or a call to get the renderer service, for testing purposes when the service isn't part of the container. This creates duplicate code in core, and a a goal of adding more test coverage means more classes will need to mock the render.

A trait should be introduce that does this, so it can be added as needed.