Create `allRowHeights` and `allRowYs` maps

[mofojed]

Right now there are visibleRows and allRows, where visibleRows is just the visible rows in the main viewport, and allRows is all the rows including floating rows. However, there is just one map visibleRowHeights that has all of the heights (including floating rows). This is pretty confusing, and we should split it out.

[dsmmcken]

There's also an issue with including hidden columns in this list, causing funny business with scrolling. Not sure if that can also be addressed.