[Firebase AI] Add x-ios-bundle-identifier header to requests

[google-labs-jules]

Added the x-ios-bundle-identifier header to GenerativeAIService and LiveSessionService requests to support iOS application API key restrictions. This requires callers to set the x-ios-bundle-identifier header to match one of the iOS Bundle IDs specified for the API key. This addresses #15475.

Important: We still strongly recommend the use of Firebase AppCheck instead of, or in addition to, API key restrictions.

[gemini-code-assist]

Code Review

This pull request correctly adds the x-ios-bundle-identifier header to support API key restrictions for iOS applications. The changes are applied to GenerativeAIService and LiveSessionService, and the unit tests have been updated accordingly. I've identified a small code duplication in GenerativeAIService.swift and a minor inconsistency in LiveSessionService.swift. Addressing these points will improve the code's clarity and maintainability.

[andrewheard]

Verified locally that requests missing the header produce API_KEY_IOS_APP_BLOCKED without the header and this fixes the error.

Full Response

{
  "error": {
    "code": 403,
    "message": "Requests from this iOS client application com.google.firebase.FirebaseAITestApp are blocked.",
    "status": "PERMISSION_DENIED",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.ErrorInfo",
        "reason": "API_KEY_IOS_APP_BLOCKED",
        "domain": "googleapis.com",
        "metadata": {
          "iosBundleId": "com.google.firebase.FirebaseAITestApp",
          "consumer": "projects/{project_number}",
          "service": "firebasevertexai.googleapis.com"
        }
      },
      {
        "@type": "type.googleapis.com/google.rpc.LocalizedMessage",
        "locale": "en-US",
        "message": "Requests from this iOS client application com.google.firebase.FirebaseAITestApp are blocked."
      }
    ]
  }
}

[google-labs-jules]

Verified locally that requests missing the header produce API_KEY_IOS_APP_BLOCKED without the header and this fixes the error.

Full Response

{
  "error": {
    "code": 403,
    "message": "Requests from this iOS client application com.google.firebase.FirebaseAITestApp are blocked.",
    "status": "PERMISSION_DENIED",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.ErrorInfo",
        "reason": "API_KEY_IOS_APP_BLOCKED",
        "domain": "googleapis.com",
        "metadata": {
          "iosBundleId": "com.google.firebase.FirebaseAITestApp",
          "consumer": "projects/{project_number}",
          "service": "firebasevertexai.googleapis.com"
        }
      },
      {
        "@type": "type.googleapis.com/google.rpc.LocalizedMessage",
        "locale": "en-US",
        "message": "Requests from this iOS client application com.google.firebase.FirebaseAITestApp are blocked."
      }
    ]
  }
}

Thanks for verifying!