More glimmer tests

[chancancode]

This is the initial work to implement the shared testing infrastructure between ember-htmlbars and ember-glimmer.

Quoting @wycats 😗

It is worth noting that the ember-glimmer tests are using Ember.View and Ember.Component. In order to make these tests pass, we hit a failing test that confirms that the view registry is empty, which means that (1) the view registry was getting populated, and (2) we had to empty it. There's still quite a bit left to do, of course, but this integration is the real deal.

Next steps:

• Symlink this test file and the shared utils to ember-htmlbars, implement the htmlbars version of the helpers, and make it pass in both packages.
• Start porting existing tests into the new format and repeat the symlink step.

[rwjblue]

@Serabe - This seems related to your recent PR, mind taking a look?

[wycats]

Once we have more tests written this way, we would definitely love to work with @Serabe to get the same style working in more places.