Implement Experimental Mode Rehydrate properly using modules for modern Ember

The way this render mode was implemented before was to inject a vendor file that monkey-patches Ember https://github.com/ember-fastboot/ember-cli-fastboot/blob/v4.1.2/packages/ember-cli-fastboot/vendor/experimental-render-mode-rehydrate.js

This really isn't the right way to do things with modern ember 🙈 we need to make sure that we're importing a module properly and possibly setting module-scope data to tell it to use the new render-mode and not rely on monkey-patching classes 👍