Provide an extendable template registry

[bertdeblock]

The current "standard" is to provide an extendable template registry via <addon-name>/template-registry.

Usage:

import '@glint/environment-ember-loose';
import type FreestyleRegistry from 'ember-freestyle/template-registry';

declare module '@glint/environment-ember-loose/registry' {
  export default interface Registry extends FreestyleRegistry {
    // ...
  }
}

[lukemelia]

Looks good. I guess this would consitute a breaking change.

[lukemelia]

Looks good. I guess this would consitute a breaking change.

Which I see you have already labeled it as! 👍