Feature Request - BarAreaData: cutOffX

BarAreaData has a value for cutOffY but it would also be useful in some applications to have cutOffX to fill below the bar up to a certain X value.

I tried to split in to multiple lines but sometimes the cut-off is between 2 of my known x values.

Start by locating BarAreaData and tracing how the existing cutOffY value is handled when the bar area is filled. Determine how a cut-off between known x values should be represented, then verify the fill reaches that X value without splitting the data. Add coverage for the new behavior, including a cut-off between two known x values.

Written by the indexing model from the issue text.