Point x and y accessors about d3-polygon

[Fil]

I would prefer to keep the API very lightweight, unless we really can boost things a lot.

To avoid creating intermediate arrays you might extend the nodes like so:
on("tick", () => { for (const d of nodes) d => d[0]=d.x, d[1]=d.y; })

(Note that the hull you retrieve is then composed of the original nodes, not just [x,y] points.)