Start adding a unified shaper access infrastructure

Add global shape_plan.  Unused so far.

src/hb-coretext.cc

diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index c99ffc4..6e09c5e 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -24,7 +24,8 @@
  * Mozilla Author(s): Jonathan Kew
  */
 
-#include "hb-private.hh"
+#define HB_SHAPER coretext
+#include "hb-shaper-private.hh"
 
 #define GlyphID GlyphID_mac
 #include <ApplicationServices/ApplicationServices.h>
@@ -32,9 +33,6 @@
 
 #include "hb-coretext.h"
 
-#include "hb-ot-name-table.hh"
-#include "hb-ot-tag.h"
-
 #include "hb-font-private.hh"
 #include "hb-buffer-private.hh"