Alternative implementation of get_unique_node_name for https://github.com/ros2/geometry2/pull/182

get_unique_node_name

std::string get_unique_node_name()
{
  const static std::string chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
  static std::random_device rd;
  static std::minstd_rand g{rd()};

  // The uniform_int_distribution takes a closed interval of [a, b]; since that
  // would include the \0, we remove one from our string length.
  static std::uniform_int_distribution<std::string::size_type> pick(0, chars.length() - 1);

  std::string s("static_transform_publisher_");

  size_t orig_length = s.length();
  s.resize(orig_length + 16);

  for (size_t i = orig_length; i < s.length(); ++i) {
    s[i] = chars[pick(g)];
  }

  return s;
}