cogl: Move CoglScanout declarations from onscreen to types

While closely related, types appears to be the more appropriate place
these days.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3559>

cogl/cogl/cogl-onscreen.h

@@ -45,8 +45,6 @@
 
 G_BEGIN_DECLS
 
-typedef struct _CoglScanout CoglScanout;
-
 #define COGL_TYPE_ONSCREEN (cogl_onscreen_get_type ())
 COGL_EXPORT
 G_DECLARE_DERIVABLE_TYPE (CoglOnscreen, cogl_onscreen,
@@ -85,15 +83,6 @@ struct _CoglOnscreenClass
   int (* get_buffer_age) (CoglOnscreen *onscreen);
 };
 
-#define COGL_SCANOUT_ERROR (cogl_scanout_error_quark ())
-COGL_EXPORT GQuark
-cogl_scanout_error_quark (void);
-
-typedef enum _CoglScanoutError
-{
-  COGL_SCANOUT_ERROR_INHIBITED,
-} CoglScanoutError;
-
 /**
  * cogl_onscreen_show:
  * @onscreen: The onscreen framebuffer to make visible

cogl/cogl/cogl-types.h

@@ -425,4 +425,20 @@ typedef enum
   COGL_STEREO_RIGHT
 } CoglStereoMode;
 
+typedef struct _CoglScanout CoglScanout;
+
+#define COGL_SCANOUT_ERROR (cogl_scanout_error_quark ())
+
+/**
+ * CoglScanoutError:
+ * @COGL_SCANOUT_ERROR_INHIBITED: Scanout inhibited
+ */
+typedef enum _CoglScanoutError
+{
+  COGL_SCANOUT_ERROR_INHIBITED,
+} CoglScanoutError;
+
+COGL_EXPORT GQuark
+cogl_scanout_error_quark (void);
+
 G_END_DECLS