cogl-framebuffer: Add a flag to skip flushing the clip state

This adds a flag to avoid flushing the clip state when flushing the
framebuffer state. This will be used by the journal to manage its own
clip state flushing.

cogl/cogl-framebuffer-private.h

@@ -122,6 +122,9 @@ typedef enum _CoglFramebufferFlushFlags
    * be called for framebuffer->modelview_stack, and the modelview_stack will
    * also be marked as dirty. */
   COGL_FRAMEBUFFER_FLUSH_SKIP_MODELVIEW =     1L<<0,
+  /* Similarly this flag implies you are going to flush the clip state
+     yourself */
+  COGL_FRAMEBUFFER_FLUSH_SKIP_CLIP_STATE =    1L<<1
 } CoglFramebufferFlushFlags;
 
 void