build: Remove the config.h inclusion from all public headers

Do not include it at header side as it is not part of the installed headers.

Only keep it in cogl-gl-headers.h as it is a private header.

Add it to all the source files that depend on it.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3593>

src/tests/clutter-test-utils.h

@@ -19,8 +19,6 @@
  * License along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include "config.h"
-
 #pragma once
 
 #define __CLUTTER_H_INSIDE__