Apply 'liga' for vertical writing mode too

Apparently that's what Kazuraki uses to form vertical ligatures,
which suggests that it's what Adobe does.

src/hb-ot-shape.cc

@@ -35,6 +35,7 @@
 
 hb_tag_t common_features[] = {
   HB_TAG('c','c','m','p'),
+  HB_TAG('l','i','g','a'),
   HB_TAG('l','o','c','l'),
   HB_TAG('m','a','r','k'),
   HB_TAG('m','k','m','k'),
@@ -46,7 +47,6 @@ hb_tag_t horizontal_features[] = {
   HB_TAG('c','l','i','g'),
   HB_TAG('c','u','r','s'),
   HB_TAG('k','e','r','n'),
-  HB_TAG('l','i','g','a'),
 };
 
 /* Note: