Evaluate exporting metrics from perf_hooks

[mmarchini]

Node.js has a Performance Hooks API to expose internal runtime metrics to the application. Some metrics we calculate in this package are also exposed there (for example, gc.pause) and others could be useful. There are also new metrics coming, like monitorEventLoopDelay and monitorEventLoopIdleness.

By using Performance Hooks, we might be able to reduce (and maybe drop) dependency on C++ code in the future, making major Node.js bumps easier.

[brharrington]

I think we looked at it before and one of the issues is it didn't work with all the versions of node we needed to support (6+). It looks like this project now lists >=10.0.0, so maybe it is more viable now.