[devtools] qunit: update to 1.18.0 (closes #5533333) * the logging API has changed (register callbacks instead of setting attributes on the QUnit object) * the logging callbacks all have a single "details" object argument * the "main" div was renamed to "qunit-fixture" (this change is responsible for all the churn in our own JS test files) * QUnit can now build the DOM elements it needs for reporting from a single "qunit" div