This adds a cogl_texture_2d_new_from_file() api since we are planning to
remove cogl_texture_new_from_file() but don't want to loose the
convenience it had.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 10e91aa513123ed277a8d45976f8d75445d7dc9c)
aa92110f83
