willTransition and didTransition are removed in favor of router service events in Ember 4. Guide here. We should start showing the router events instead.

We are using them on this page: https://guides.emberjs.com/release/routing/preventing-and-retrying-transitions

This PR can be opened and merged as soon as its ready. We don't have to wait for Ember 4, but we do need it in place by then.