[SYSTEMDS-3762] Cumulative Row Aggregates and Rewrites

[sandrathena]

implemented FIXME in spark instruction

[sandrathena]

Here are our experiment diagrams:

[sandrathena]

Here are our detailed experiment diagrams:

[mboehm7]

Thanks for sharing theses experimental results @sandrathena. The results look good and are absolutely in the range what we would expect - the core rowcumsum is slightly faster because of sequential access to the row-major layout, and the rewrite avoids the costly transpose.