ember-cli should determine LCA host and host addons for lazy engines

[brendenpalmer]

Currently ember-engines is responsible for computing its host addons for deduplication purposes. To do this it uses a utility, findLCAHost, to find a common host for all lazy engines by the same name in the project: https://github.com/ember-engines/ember-engines/blob/master/packages/ember-engines/lib/utils/find-lca-host.js.

This issue is to track moving this functionality to ember-cli, so that ember-engines can later be updated to consume it from ember-cli if it exists, otherwise it'll fall back to its internal implementation. The idea is that with #9487, it's preferable to not have to duplicate the logic in multiple contexts, so that there's a single source of truth.