cogl: Remove CoglBool, use gboolean instead

This basically reverts commit 54735dec, which tried to avoid the
GLib-defined types in favor the standard C ones. One exception to this
is the bool type, for which the commit introduces a new type CoglBool.

Let's just get rid of this type in favor of having consistency with the
GLib types. Note by the way that neither CoglBool nor gboolean (which
has a size of `int`) are completely compatible with bool (size `char`).

https://gitlab.gnome.org/GNOME/mutter/merge_requests/321

cogl/cogl-path/cogl-path-functions.h

@@ -96,7 +96,7 @@ cogl_path_copy (CoglPath *path);
  *
  * Since: 2.0
  */
-CoglBool
+gboolean
 cogl_is_path (void *object);
 
 #define cogl_path_move_to cogl2_path_move_to