Implement hb_shape_plan_get_shaper()

Untested.

src/hb-shape-plan.cc

diff --git a/src/hb-shape-plan.cc b/src/hb-shape-plan.cc
index d73a828..7735d4e 100644
--- a/src/hb-shape-plan.cc
+++ b/src/hb-shape-plan.cc
@@ -49,6 +49,7 @@
 	    HB_SHAPER_DATA (shaper, shape_plan) = \
 	      HB_SHAPER_DATA_CREATE_FUNC (shaper, shape_plan) (shape_plan, user_features, num_user_features); \
 	    shape_plan->shaper_func = _hb_##shaper##_shape; \
+	    shape_plan->shaper_name = #shaper; \
 	    return; \
 	  } \
 	} HB_STMT_END
@@ -120,6 +121,7 @@
     HB_SEGMENT_PROPERTIES_DEFAULT, /* props */
 
     NULL, /* shaper_func */
+    NULL, /* shaper_name */
 
     {
 #define HB_SHAPER_IMPLEMENT(shaper) HB_SHAPER_DATA_INVALID,
@@ -298,3 +300,8 @@
 
   return hb_shape_plan_reference (shape_plan);
 }
+
+const char *
+hb_shape_plan_get_shaper (hb_shape_plan_t *shape_plan)
+{
+}