rendernode: Put typedef into gsktypes.h

Makes includes simpler for headers that want to use GskRenderNode.

gsk/gskrendernode.h

@@ -35,7 +35,6 @@ G_BEGIN_DECLS
 
 #define GSK_SERIALIZATION_ERROR       (gsk_serialization_error_quark ())
 
-typedef struct _GskRenderNode           GskRenderNode;
 typedef struct _GskColorStop            GskColorStop;
 typedef struct _GskShadow               GskShadow;
 

gsk/gsktypes.h

@@ -29,6 +29,7 @@ typedef struct _GskPath                 GskPath;
 typedef struct _GskPathBuilder          GskPathBuilder;
 typedef struct _GskPathPoint            GskPathPoint;
 typedef struct _GskRenderer             GskRenderer;
+typedef struct _GskRenderNode           GskRenderNode;
 typedef struct _GskStroke               GskStroke;
 typedef struct _GskTransform            GskTransform;