Function combine

include/behaviortree_cpp/contrib/json.hpp:6004–6008

boost::hash_combine

// boost::hash_combine
inline std::size_t combine(std::size_t seed, std::size_t h) noexcept
{
    seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
    return seed;
}

/*!
@brief hash a JSON value