napi_jsrt: Investigate usefulness of adjusting external memory

[jackhorton]

• napi_jsrt stub:

  node-chakracore/src/node_api_jsrt.cc

  Line 2520 in 070fe0f

  napi_status napi_adjust_external_memory(napi_env env,

• node pull request: n-api: adds function to adjust external memory node#14310

@chris--young If you are already looking into this, let us know anything you find!