[ot] Add Hangul shaper

Not exhaustively tested, but I think I got the intended logic
right.

The logic can perhaps be simplified.  Maybe we should disabled
normalization with this shaper.  Then again, for now focusing on
correctness.
diff --git a/src/hb-private.hh b/src/hb-private.hh
index 4b72260..680b21e 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -808,6 +808,12 @@
 }
 
 template <typename T> static inline bool
+hb_in_ranges (T u, T lo1, T hi1, T lo2, T hi2)
+{
+  return hb_in_range (u, lo1, hi1) || hb_in_range (u, lo2, hi2);
+}
+
+template <typename T> static inline bool
 hb_in_ranges (T u, T lo1, T hi1, T lo2, T hi2, T lo3, T hi3)
 {
   return hb_in_range (u, lo1, hi1) || hb_in_range (u, lo2, hi2) || hb_in_range (u, lo3, hi3);