This adds a cogl_renderer_foreach_output() function that can be used to
iterate the display outputs for a particular renderer.
This also updates cogl-info to use this new api so it can dump out all
the output information.
Reviewed-by: Owen W. Taylor <otaylor@fishsoup.net>
(cherry picked from commit a2abf4c4c1fd5aeafd761f965d07a0fe9a362afc)