[firebase_auth] Allow setting displayName on creation of account

[Minituff]

I am trying to use Firebase Cloud Functions to create a user account in my Firestore database when a user signs up. The only trigger available in Cloud Functions is when a user is created (docs here). The problem is, I can only create a user with a username and password-- a displayName cannot be provided.
Therefore, this cloud function will be triggered with no displayName provided.

Below is the source code from the firebase_auth package, where you can see there is no option to add the displayName on creation of a user.

  /// Tries to create a new user account with the given email address and
  /// password.
  ///
  /// A [FirebaseAuthException] maybe thrown with the following error code:
  /// - **email-already-in-use**:
  ///  - Thrown if there already exists an account with the given email address.
  /// - **invalid-email**:
  ///  - Thrown if the email address is not valid.
  /// - **operation-not-allowed**:
  ///  - Thrown if email/password accounts are not enabled. Enable
  ///    email/password accounts in the Firebase Console, under the Auth tab.
  /// - **weak-password**:
  ///  - Thrown if the password is not strong enough.
  Future<UserCredential> createUserWithEmailAndPassword({
    required String email,
    required String password,
  }) async {
    return UserCredential._(
      this,
      await _delegate.createUserWithEmailAndPassword(email, password),
    );
  }

It would be nice if you could add an optional displayName to this function so that the Cloud Function can have the information needed.