Tooltip following y-axis

[rubenjonk]

Summary

Using the tooltip currently only "follows" your cursor across the x-axis. When working with data where the y-axis is shared (such as height data), it would be great to have the tooltip follow the y-axis.

API Changes

chart: { main_axis: 'x' (default, can be changed to y) }

Intended Use Case

When having data where the main shared axis is the y-axis, such as height and depth measurements. Having the height on the y-axis is visually logical, since we are working vertically.