Ember 3.27 and/or embroider/test-setup 0.40 breaks ec-addon-docs

[elwayman02]

Two of my projects using ec-addon-docs are failing to render when deployed, with the same error surfacing when upgrading ember-source to 3.27 or embroider/test-setup to 0.40.

See: emberjs/ember.js#19538 and embroider-build/embroider#805

[elwayman02]

Incidentally, my doc sites that don't use ec-addon-docs have not experienced these issues, so something about the way ec-addon-docs is built specifically runs afoul of the bugs introduced in those versions.

[RobbieTheWagner]

@elwayman02 I believe that ember-modal-dialog is the source of a lot of our embroider woes.

[RobbieTheWagner]

I think things should be working now, but let me know if they are not.