cogl: Port Primitive away from CoglObject

- The associated CoglAttribute's are now stored in GPtrArray as suggested
by carlosg in
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3193?commit_id=19b619073b3c7d311c64e0a997558f943b38c94a#note_1849281
- cogl_primitive_set_attributes was dropped for "simplicity"
especially that nothing uses it.
- As this is the last remaining CoglObject subclass, the commit also drops
all the CoglObject related macros/types

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3193>

src/tests/cogl/conform/test-map-buffer-range.c

@@ -108,7 +108,7 @@ test_map_buffer_range (void)
                         tex_coord_attribute,
                         NULL);
   cogl_primitive_draw (primitive, test_fb, pipeline);
-  cogl_object_unref (primitive);
+  g_object_unref (primitive);
 
   /* Top left pixel should be the one that is replaced to be green */
   test_utils_check_pixel (test_fb, 1, 1, 0x00ff00ff);