Add simple Hangul shaper that recomposes Jamo when feasible

Previously, we were NOT actually recomposing Hangul Jamo.  We do now.
The two lines in:

test/shaping/texts/in-tree/shaper-default/script-hangul/misc/misc.txt

Now render the same with the UnDotum.ttf font.  Previously the second
linle was rendering boxes.

We can also start applying OpenType Jamo features later.  At this time,
I have no idea how the 'ljmo', 'vjmo', 'tjmo' features are supposed to
work.  Maybe someone can explain them to me?

src/hb-ot-shape-complex-misc.cc

@@ -53,3 +53,19 @@ _hb_ot_shape_complex_setup_masks_default (hb_ot_map_t *map, hb_buffer_t *buffer)
 }
 
 
+
+void
+_hb_ot_shape_complex_collect_features_hangul (hb_ot_map_builder_t *map, const hb_segment_properties_t  *props)
+{
+}
+
+hb_ot_shape_normalization_mode_t
+_hb_ot_shape_complex_normalization_preference_hangul (void)
+{
+  return HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_FULL;
+}
+
+void
+_hb_ot_shape_complex_setup_masks_hangul (hb_ot_map_t *map, hb_buffer_t *buffer)
+{
+}

src/hb-ot-shape-complex-private.hh

@@ -50,6 +50,7 @@
 #define HB_COMPLEX_SHAPERS_IMPLEMENT_SHAPERS \
   HB_COMPLEX_SHAPER_IMPLEMENT (default) /* should be first */ \
   HB_COMPLEX_SHAPER_IMPLEMENT (arabic) \
+  HB_COMPLEX_SHAPER_IMPLEMENT (hangul) \
   HB_COMPLEX_SHAPER_IMPLEMENT (indic) \
   /* ^--- Add new shapers here */
 
@@ -69,6 +70,7 @@ hb_ot_shape_complex_categorize (const hb_segment_properties_t *props)
     default:
       return hb_ot_complex_shaper_default;
 
+
     /* Unicode-1.1 additions */
     case HB_SCRIPT_ARABIC:
     case HB_SCRIPT_MONGOLIAN:
@@ -82,6 +84,17 @@ hb_ot_shape_complex_categorize (const hb_segment_properties_t *props)
 
       return hb_ot_complex_shaper_arabic;
 
+
+    /* Unicode-1.1 additions */
+    case HB_SCRIPT_HANGUL:
+
+      return hb_ot_complex_shaper_hangul;
+
+
+
+    /* ^--- Add new shapers here */
+
+
 #if 0
     /* Note:
      *
@@ -191,8 +204,6 @@ hb_ot_shape_complex_categorize (const hb_segment_properties_t *props)
     case HB_SCRIPT_TAKRI:
 
       return hb_ot_complex_shaper_indic;
-
-    /* ^--- Add new shapers here */
   }
 }