Add `Date::New` for `std::chrono::system_clock::time_point`

[cacharle]

It would be nice to be able to create a Date from a std::chrono::system_clock::time_point

Here is my (not so great) implementation):

Napi::Value timePointToJsDate(Napi::Env env, std::chrono::system_clock::time_point tp)
{
    using namespace std::chrono;
    auto ms static_cast<double>(duration_cast<milliseconds>(tp.time_since_epoch()).count());
    return Date::New(env, ms);
}