Add HB_NO_OT_SHAPE_COMPLEX_VOWEL_CONSTRAINTS

Part of https://github.com/harfbuzz/harfbuzz/issues/1652

src/hb-ot-shape-complex-vowel-constraints.cc

@@ -34,6 +34,9 @@ _hb_preprocess_text_vowel_constraints (const hb_ot_shape_plan_t *plan HB_UNUSED,
 				       hb_buffer_t              *buffer,
 				       hb_font_t                *font HB_UNUSED)
 {
+#if defined(HB_NO_OT_SHAPE_COMPLEX_VOWEL_CONSTRAINTS)
+  return;
+#endif
   if (buffer->flags & HB_BUFFER_FLAG_DO_NOT_INSERT_DOTTED_CIRCLE)
     return;