Major Description
`OptimizeSkewInRebalancePartitions` now is applied if the `RebalancePartitions` is the root node, but sometimes, we expect a local sort after do RebalancePartitions that can improve the compression ratio.
After SPARK-36184, we make validate easy that whether the rule introduces extra shuffle or not and the output partitioning is ensured by `AQEShuffleReadExec.outputPartitioning`.
So it is safe to make `OptimizeSkewInRebalancePartitions` support optimize non-root node.
