Function is_structured

include/behaviortree_cpp/contrib/json.hpp:20610–20613

@brief return whether type is structured @sa https://json.nlohmann.me/api/basic_json/is_structured/

    /// @brief return whether type is structured
    /// @sa https://json.nlohmann.me/api/basic_json/is_structured/
    constexpr bool is_structured() const noexcept
    {
        return is_array() || is_object();
    }

    /// @brief return whether value is null
    /// @sa https://json.nlohmann.me/api/basic_json/is_null/