DEV: Print usedJSHeapSize to the console after QUnit run (PR #14462)

This is console.log'd to the browser console. run-qunit will print this to stdout. testem will not, so a custom reporter is implemented to print this message.

The --enable-precise-memory-info is added so that chrome provides high-resolution memory information. This API is not supported by firefox. The logic will degrade gracefully.

TestEm output:

Built project successfully. Stored in "/var/folders/c7/3jzsz23s16l3_jtzrttkxwfw0000gn/T/tests-dist-2021828-53762-zyrvye.43hq".

Used JS Heap Size: 0.080GB

# tests 5
# pass  5
# skip  0
# todo  0
# fail  0

# ok
✨  Done in 21.07s.

Run-qunit output:

↪ Integration | Component | Widget | discourse-poll-option::multi, selected [✔]

Used JS Heap Size: 0.232GB

Slowest tests