N-API: Add method to get own properties

[mhdawson]

• Version: ALL
• Platform: ALL
• Subsystem: ALL

We need a new function to allow add-ons to get own properties consistently across versions:

```C++
napi_status napi_get_own_property(napi_env e,
                                  napi_value o,
                                  napi_propertyname p,
                                  napi_value* result);

which never walks up the prototype chain.

We also need to validate/ensure that napi_get_property() always walks up the prototype chain.

The N-API team will get to this based on priorities, but this is a good place for others to contribute as well. If you start working on this, assign the issue to yourself and add a comment that you are working on it.

[cjihrig]

Working on this.

[cjihrig]

@mhdawson I added a test for napi_get_property() walking the prototype chain in #13961. I'm questioning if we really need a napi_get_own_property() though. I understand the use case, but wouldn't it be better to have napi_has_own_property(), which would correspond to Object.prototype.hasOwnProperty()?

[cjihrig]

@mhdawson ping ^

[cjihrig]

Closing this out as the test has been added and napi_has_own_property() should be enough for users to build a get_own_property() as needed.