Add debug notes for calls to glViewport()

In order to validate the sequence of:

        XResizeWindow
        ConfigureNotify
        glViewport

that should happen on X11 we need to add debug annotations to the
calls to glViewport() done through COGL.

clutter/cogl/common/cogl.c

@@ -500,6 +500,7 @@ cogl_viewport (guint width,
 {
   _COGL_GET_CONTEXT (ctx, NO_RETVAL);
 
+  COGL_NOTE (MISC, "glViewport(0, 0, %u, %u)", width, height);
   GE( glViewport (0, 0, width, height) );
 
   ctx->viewport_width = width;