[aat] If shaping via morx, don't adjust mark positioning when zeroing widths.

src/hb-ot-shape.cc

@@ -193,6 +193,12 @@ hb_ot_shape_planner_t::compile (hb_ot_shape_plan_t           &plan,
 				   script_fallback_mark_positioning;
 
 #ifndef HB_NO_AAT_SHAPE
+  /* If we're using morx shaping, we cancel mark position adjustment because
+     Apple Color Emoji assumes this will NOT be done when forming emoji sequences;
+     https://github.com/harfbuzz/harfbuzz/issues/2967. */
+  if (plan.apply_morx)
+    plan.adjust_mark_positioning_when_zeroing = false;
+
   /* Currently we always apply trak. */
   plan.apply_trak = plan.requested_tracking && hb_aat_layout_has_tracking (face);
 #endif