n-api: test and doc napi_throw() of a primitive

Ensure that napi_throw() is able to throw a primitive value, and
document that it is able to throw any JavaScript value.

Fixes: https://github.com/nodejs/abi-stable-node/issues/309
PR-URL: https://github.com/nodejs/node/pull/20428


Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>