n-api: keep napi_env alive while it has finalizers

Manage the napi_env refcount from Finalizer instances, as the
finalizer may refer to the napi_env until it is deleted.

Fixes: https://github.com/nodejs/node/issues/31134
Fixes: https://github.com/node-ffi-napi/node-ffi-napi/issues/48
PR-URL: https://github.com/nodejs/node/pull/31140


Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>