perf_hooks: add event loop delay sampler

Inspired by (and code borrowed from) https://github.com/mafintosh/event-loop-delay

/cc @mafintosh @mcollina

Adds a simple event loop delay sampler to perf_hooks.

See included test for example use.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines