`find` and `findAll` should allow for finding elements outside the root

When dealing with addons like ember-pikaday or ember-wormhole, it can be useful to allow for locating an element outside the root element of the test.

My proposal would be to allow a second parameter, like qunit-dom, that allows you to override the “root element” to search.

If this is something you’d be interested in supporting, I’m happy to make a PR for it!

Note: I’m not suggesting we add the root-override behavior to all helpers; it’s easy enough to, for example, compose two together if you need to click something outside the root:

const button = await find('.some-button', document.body);
await click(button);

[rwjblue]

Hmm, why is a change needed here? What would adding a context parameter provide that “using the platform” doesn’t?

const button = document.querySelector('.some-button');
await click(button);

[cibernox]

Although this was closed I’d like to provide a reason why by default the test helpers should be scoped to the testing container, is that QUnit is working in parallel execution: https://twitter.com/trentmwillis/status/1050519960689115136

Having test selectors scoped to the testing containers puts us on a good position to have several test containers running different tests at the same time, each one triggering events and performing assertions on their own app.