[TooltipContext] Support `quadtree` mode for Line / Area chart use cases

[techniq]

Currently we use bisect-x as the default tooltip mode for LineChart and AreaChart.

If the implementation supported ignoring the y channel (or x) by returning a constant such as 0, then quadtree could also be used.

Might then might want to consider changing AreaChart, LineChart, and ScatterChart to use quadtree by default (faster than voronoi, and possibly bisect-x)

• AreaChart (currently bisect-x)
• LineChart (currently bisect-x)
• ScatterChart (currently voronoi)