n-api: implement napi_run_script

Fixes: https://github.com/nodejs/abi-stable-node/issues/51
PR-URL: https://github.com/nodejs/node/pull/15216


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell.gmail.com>
Reviewed-By: Michael Dawson <mhdawson@ca.ibm.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>