Make cogl_framebuffer_get_width/height experimental public API

It's generally useful to be able to query the width and height of a
framebuffer and we expect to need this in Clutter when we move the
eglnative backend code into Cogl since Clutter will need to read back
the fixed size of the framebuffer when realizing the stage.

cogl/cogl-framebuffer.h

@@ -43,6 +43,14 @@ gboolean
 cogl_framebuffer_allocate (CoglFramebuffer *framebuffer,
                            GError **error);
 
+#define cogl_framebuffer_get_width cogl_framebuffer_get_width_EXP
+int
+cogl_framebuffer_get_width (CoglFramebuffer *framebuffer);
+
+#define cogl_framebuffer_get_height cogl_framebuffer_get_height_EXP
+int
+cogl_framebuffer_get_height (CoglFramebuffer *framebuffer);
+
 #define cogl_framebuffer_swap_buffers cogl_framebuffer_swap_buffers_EXP
 void
 cogl_framebuffer_swap_buffers (CoglFramebuffer *framebuffer);