test: improve test coverage for n-api

Add basic tests for handle scopes as code coverage
reports that we are not covering these with the existing
tests.

Backport-PR-URL: https://github.com/nodejs/node/pull/19447
PR-URL: https://github.com/nodejs/node/pull/12327


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>