[OT] Apply 'rclt' feature in horizontal mode

'rclt' is "Required Contextual Forms" being proposed by Microsoft.
It's like 'calt', but supposedly always on.  We apply 'calt' anyway,
and now apply this too.

src/hb-ot-shape.cc

@@ -54,6 +54,7 @@ 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('r','c','l','t'),
 };
 
 /* Note: