Rewrite grapheme-formation in terms of new work
Also, don't attach ZWNJ to previous cluster. Closer to Unicode graphemes.
diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index 8b120aa..ab04d72 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -626,7 +626,7 @@
CGFloat y_mult = (CGFloat) font->y_scale / ct_font_size;
/* Attach marks to their bases, to match the 'ot' shaper.
- * Adapted from hb-ot-shape:hb_form_clusters().
+ * Adapted from a very old version of hb-ot-shape:hb_form_clusters().
* Note that this only makes us be closer to the 'ot' shaper,
* but by no means the same. For example, if there's
* B1 M1 B2 M2, and B1-B2 form a ligature, M2's cluster will
