Imported types are converted into strings in literal expression

[cengels]

The following code:

// types.ts
export type MyType = 'one' | 'two' | 'three';

// interface.ts
import { MyType } from './types';

export interface MyObject {
    value: `_${MyType}`;
}

unexpectedly results in a schema where value is simply { "type": "string" } instead of

{
    "enum": [
      "_one",
      "_two",
      "_three"
    ],
    "type": "string"
  }
}

This seems to happen because extractLiterals() currently only considers AliasTypes, not DefinitionTypes.