setupLink() is broken for engines

[gossi]

As we figured, we weren't able to use setupLink() from within engines. @buschtoens did a run-down of this (credits to him, I'm just writing it down):

We are hit by this: emberjs/ember.js#11173 (comment)

ember-link/addon-test-support/setup-link.ts

Lines 9 to 16 in 2db4148

	assert(
	'ember-link.setupLink: You have already called `setupLink` once',
	!this.owner.hasRegistration('service:link-manager') ||
	!(
	this.owner.lookup('service:link-manager') instanceof
	TestInstrumentedLinkManagerService
	)
	);

places the normal LinkManagerService in the container.cache and container.factoryManagerCache.
Then the following owner.unregister(…) apparently only removes the registration, but not the instance in the container.cache.

There fix was added to ApplicationInstance, but the owner in our test is not a fully-fledged ApplicationInstance: https://github.com/emberjs/ember.js/pull/12680/files

This seems to be an upstream bug in @ember/test-helpers, here is the trace:

We don’t have an application in render tests, but a resolver, so we hit L57 in
https://github.com/emberjs/ember-test-helpers/blob/a4f710420e8dfba1a4245981483d7cbb5dcc865e/addon-test-support/%40ember/test-helpers/build-owner.ts#L41-L60

Which then builds a registry and owner on its own terms.
https://github.com/emberjs/ember-test-helpers/blob/a4f710420e8dfba1a4245981483d7cbb5dcc865e/addon-test-support/@ember/test-helpers/-internal/build-registry.ts

This of course lacks the unregister patch:
https://github.com/emberjs/ember.js/blob/0da7fedd3767668e7fb01b50757f1a636782fb54/packages/%40ember/engine/instance.ts#L162-L167

[buschtoens]

Thanks for copying this over and also thanks for prepping a PR. 😊

Since I consider this a bug in @ember/test-helpers, I've sent in this PR to fix it upstream: emberjs/ember-test-helpers#1216

Hopefully it will be accepted, then we can skip #715. Still thank you for working on this. 🙏

[buschtoens]

My PR was merged and released as 2.8.0.