doc: updated guidance for n-api changes

Add js_native_api.h and js_native_api_types.h to the list
of files covered by the N-API guidance as these were
broken out of the files referenced.

Signed-off-by: Michael Dawson <michael_dawson@ca.ibm.com>

PR-URL: https://github.com/nodejs/node/pull/32721


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>