[morx] Reverse graphemese, not whole buffer

Fixes https://github.com/harfbuzz/harfbuzz/issues/3314
Supersedes https://github.com/harfbuzz/harfbuzz/pull/3315

src/hb-aat-layout-morx-table.hh

@@ -1038,12 +1038,12 @@ struct Chain
 	goto skip;
 
       if (reverse)
-	c->buffer->reverse ();
+	_hb_ot_layout_reverse_graphemes (c->buffer);
 
       subtable->apply (c);
 
       if (reverse)
-	c->buffer->reverse ();
+	_hb_ot_layout_reverse_graphemes (c->buffer);
 
       (void) c->buffer->message (c->font, "end chainsubtable %d", c->lookup_index);
 

src/hb-ot-layout.hh

@@ -359,6 +359,12 @@ _hb_grapheme_group_func (const hb_glyph_info_t& a HB_UNUSED,
 #define foreach_grapheme(buffer, start, end) \
 	foreach_group (buffer, start, end, _hb_grapheme_group_func)
 
+static inline void
+_hb_ot_layout_reverse_graphemes (hb_buffer_t *buffer)
+{
+  buffer->reverse_groups (_hb_grapheme_group_func,
+			  buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS);
+}
 
 static inline bool
 _hb_glyph_info_is_unicode_format (const hb_glyph_info_t *info)

src/hb-ot-shape.cc

@@ -628,20 +628,7 @@ hb_ensure_native_direction (hb_buffer_t *buffer)
       (HB_DIRECTION_IS_VERTICAL   (direction) &&
        direction != HB_DIRECTION_TTB))
   {
-
-    if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS)
-      foreach_grapheme (buffer, start, end)
-      {
-	buffer->merge_clusters (start, end);
-	buffer->reverse_range (start, end);
-      }
-    else
-      foreach_grapheme (buffer, start, end)
-	/* form_clusters() merged clusters already, we don't merge. */
-	buffer->reverse_range (start, end);
-
-    buffer->reverse ();
-
+    _hb_ot_layout_reverse_graphemes (buffer);
     buffer->props.direction = HB_DIRECTION_REVERSE (buffer->props.direction);
   }
 }

test/shape/data/in-house/tests/macos.tests

@@ -1,3 +1,6 @@
+# https://github.com/harfbuzz/harfbuzz/issues/3314
+/System/Library/Fonts/Apple\ Color\ Emoji.ttc;;U+05D0,U+1F1FA,U+1F1F8,U+1F1EE,U+1F1F1;[u1F1EE_u1F1F1=3+800|u1F1FA_u1F1F8=1+800|.notdef=0+800]
+
 # https;//github.com/harfbuzz/harfbuzz/issues/3008
 /System/Library/Fonts/ヒラギノ丸ゴ\ ProN\ W4.ttc;--features=palt;U+FF11;[gid781=0@-78,0+842]