n-api: implement date object

Implements `napi_create_date()` as well as `napi_is_date()` to
allow working with JavaScript Date objects.

PR-URL: https://github.com/nodejs/node/pull/25917


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>