LanguageSwitchLinks frontpage behavior deviates from LanguageBlock

Problem/Motivation

If the frontpage "url" is passed through \Drupal\graphql_core_schema\Plugin\GraphQL\DataProducer\LanguageSwitchLinks::resolve() the resolved language switcher links point to the entity / path instead the frontpage.

The tests have been written using LLM support - the rest by a grumpy organic developer :)

Steps to reproduce

A query like:

query Routing {
  route(path: "/", skipFrontpageRedirect: true) {
    ... on InternalUrl {
      languageSwitchLinks {
        url {
          path
        }
        title
      }
    }
  }
}

Returns

{
  "data": {
    "route": {
      "languageSwitchLinks": [
        {
          "url": {
            "path": "/en/my-homepage"
          },
          "title": "English"
        },
        {
          "url": {
            "path": "/de/meine-homepage"
          },
          "title": "German"
        },
      ]
    }
  }
}

Instead of

{
  "data": {
    "route": {
      "languageSwitchLinks": [
        {
          "url": {
            "path": "/en"
          },
          "title": "English"
        },
        {
          "url": {
            "path": "/de"
          },
          "title": "German"
        },
      ]
    }
  }
}

Proposed resolution

Add a similar approach in \Drupal\graphql_core_schema\Plugin\GraphQL\DataProducer\LanguageSwitchLinks::resolve() as \Drupal\language\Plugin\Block\LanguageBlock::build() uses and use the <front> placeholder as url if the frontpage path is being resolved.

⚠ Since this is a behavior change I propose to make it opt-in via an optional argument keepFrontpagePath.

Remaining tasks

1. ✓ Write Code - decide on approach regarding opt-in or nah
2. ✓ Write Tests - have been written using LLM support - the rest by a grumpy organic developer :)
3. Review
4. Profit

User interface changes

None

API changes

None - so far only opt-in change planned. The introduced argument might affect code that integrates with the languageSwither DataProducer because 'keepFrontpagePath' has to be mapped in the builder.

Data model changes

None