[meta] Add hb_is_cr_convertible_to()

src/hb-meta.hh

@@ -98,6 +98,11 @@ template <typename T> using hb_remove_pointer = typename hb_match_pointer<T>::ty
 
 template <typename T> using hb_decay = hb_remove_const<hb_remove_reference<T>>;
 
+#define hb_is_cr_convertible_to(A, B) ( \
+	hb_is_same (hb_decay<A>, hb_decay<B>) && \
+	hb_is_const (A) <= hb_is_const (B) && \
+	hb_is_reference (A) >= hb_is_reference (B))
+
 
 /* std::move and std::forward */