A way to check std when converted to working under Node.js via dnt

[kitsonk]

We should consider adding a process to CI that "exports" std to Node.js via dnt to identify any issues that are specific to the code when targetting Node.js with the std library.

Ref: #1917

cc/ @dsherret

[iuioiua]

@kt3k, can this be closed now as we have the Node test runner?

[kt3k]

I think so. Let's close.

(Node.js test runner is available at: https://github.com/denoland/std/tree/71c828a079098a9a9a0d2a568dc28d511b9dfef2/_tools/node_test_runner