This is a preparation work for future creating ResultPartitionWriter via proposed ShuffleService.
Currently there exists only one ResultPartition implementation for ResultPartitionWriter interface, so the specific ResultPartition instance is easily referenced in many other classes such as Task, NetworkEnvironment, etc. Even some private methods in ResultPartition would be called directly in these reference classes.
Considering ShuffleService might create multiple different ResultPartitionWriter implementations future, then all the other classes should only reference with the interface and call the common methods. Therefore we extend the related methods in ResultPartitionWriter interface in order to cover existing logics in ResultPartition.