message: Adding GroupFriend::get_top_ref again
  Needed by realm-sync
diff: @@ -1186,6 +1186,11 @@ public:
  return group.m_alloc;
  }
  + static ref_type get_top_ref(const Group& group) noexcept
  + {
  + return group.m_top.get_ref();
  + }
  +
  static ref_type get_history_ref(Allocator& alloc, ref_type top_ref) noexcept
  {
  Array top(alloc);
  