Allow complex shapers overriding common features

In a new callback...  Currently unused by all complex shapers.

src/hb-ot-shape.cc

diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 60b028d..b5485bd 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -123,6 +123,8 @@
   else
     ADD_FEATURES (vertical_features);
 
+  hb_ot_shape_complex_override_features (planner->shaper, &planner->map, props);
+
 #undef ADD_FEATURES
 
   for (unsigned int i = 0; i < num_user_features; i++) {