auto-import / import-suggestions only work on gts files

[NullVoxPopuli]

like in #676
it seems none of the language features are available in gjs.

Demo project: https://github.com/NullVoxPopuli/is-polaris-ready-yet/

My tsconfig.json:

{
  "extends": "@tsconfig/ember/tsconfig.json",
  "glint": {
    "environment": ["ember-loose", "ember-template-imports"],
  },
  "compilerOptions": {
    // The combination of `baseUrl` with `paths` allows Ember's classic package
    // layout, which is not resolveable with the Node resolution algorithm, to
    // work with TypeScript.
    "baseUrl": ".",
    "allowJs": true,
    // Apps don't need to publish declarations
    "declaration": false,
    "paths": {
      "is-ready/tests/*": ["tests/*"],
      "is-ready/*": ["app/*"],
      "*": ["types/*"],
    },
  },
  "include": ["app/**/*", "tests/**/*", "types/**/*"],
}