Could you make ProvideError public?

## What feature would you like to see?
```java
protected interface ProvideError {
Exception getError();
}
```
[This](https://github.com/firebase/firebase-android-sdk/blob/master/firebase-storage/src/main/java/com/google/firebase/storage/StorageTask.java#L1061-L1063) interface public
## How would you use it?
Allowing it to be public, you could then create Kotlin extension on the highest generic upper bound of `StorageTask` like:
```kotlin
fun Continuation.resume(): Unit =
resumeWith(Result.success(Unit))

suspend fun StorageTask.await() = suspendCancellableCoroutine { cont ->
val l = OnCompleteListener { cont.resume() }
addOnCompleteListener(l)
cont.invokeOnCancellation { removeOnCompleteListener(l) }
}
```

Start in firebase-storage/src/main/java/com/google/firebase/storage/StorageTask.java at the ProvideError declaration linked in the issue. Check the surrounding StorageTask API and firebase-storage validation or tests, then confirm that the interface is publicly accessible without changing its methods.

Written by the indexing model from the issue text.