[auth] Not giving "password" providerId

### [REQUIRED] Step 2: Describe your environment

* Android Studio version: latest
* Firebase Component: Auth (Database, Firestore, Storage, Functions, etc)
* Component version: latest

### [REQUIRED] Step 3: Describe the problem

#### Steps to reproduce:

When sign in using email and password, the providerId is null, whereas on iOS it's "password".
First reported here:https://github.com/firebase/flutterfire/issues/12985

#### Relevant Code:

```
firebaseAuth
.signInWithEmailAndPassword(email, password)
.addOnCompleteListener(
task -> {
if (task.isSuccessful()) {
// task.getResult().getAdditionalUserInfo().getProviderId() is null
} else {
result.error(
FlutterFirebaseAuthPluginException.parserExceptionToFlutter(
task.getException()));
}
});
```