Performance improvement for some window functions

This release includes a change that improves the performance of some Spark window functions, specifically functions that do not include an ORDER BY clause or a window_frame parameter. In these cases, the system can rewrite the query to run it using an aggregate function. This change allows the query to run faster by using partial aggregation and avoiding the overhead of running window functions. The Spark configuration parameter spark.databricks.optimizer.replaceWindowsWithAggregates.enabled controls this optimization and is set to true by default. To turn this optimization off, set spark.databricks.optimizer.replaceWindowsWithAggregates.enabled to false.