[CX] Implement reverse aggregation steps in window operator

Aggregations inside window operator can be further optimized by supporting reverse steps for aggregate functions. The will improve query performance for aggregations over sliding frames (e.g. x preceding to y following) because instead of aggregating over the whole frame we'd be able to de-aggregate (apply reverse steps) for tuples that leave the frame and aggregate (forward steps) tuples the are added to the frame.