DEV: Print usedJSHeapSize to the console after QUnit run (#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.

test/run-qunit.js

@@ -42,6 +42,7 @@ async function runAllTests() {
         "--disable-dev-shm-usage",
         "--mute-audio",
         "--window-size=1440,900",
+        "--enable-precise-memory-info",
       ],
     };