Version 9.2.0

### 9.2.0
- Changes
    - Crashlytics: Fix requiring user code to reference Crashlytics when using il2cpp.
    - Firestore: Added `TransactionOptions` to control how many times a
      transaction will retry commits before failing
      ([#318](https://github.com/firebase/firebase-unity-sdk/pull/318)).
    - Database (Desktop): If the app data directory doesn't exist, create it.
      This fixes an issue with disk persistence on Linux.
    - Messaging (Android): Make sure all the resources are closed in
      `RegistrationIntentService`.
      ([#973](https://github.com/firebase/firebase-cpp-sdk/issues/973)).