Add variation coords to shape_plan proposal

This is the root cause of bug worked around in 19e77e01bc.

Still no shape plan caching for variations though.

src/hb-shape-plan.cc

@@ -481,6 +481,8 @@ hb_shape_plan_create_cached2 (hb_face_t                     *face,
     shaper_list,
     user_features,
     num_user_features,
+    coords,
+    num_coords,
     nullptr
   };