monotone X for lineY?

[Fil]

We could have an option to sort the scaled X channel of a lineY—currently the sort option sorts the unscaled channel, which makes it difficult to sort x if it is ordinal with an arbitrary domain. It's also difficult to sort a line connecting groups. For an example see https://observablehq.com/d/50d4e8b7d32bf564#cell-102

Plot.plot({
  marginLeft: 70,
  x: {
    line: true,
    domain: ["Oceania", "Africa", "Americas", "Asia", "Europe"] // setting the order manually by specifying the array
  },
  y: {
    line: true
  },
  marks: [
    Plot.barY(
      countries,
      Plot.groupX({ y: "max" }, { y: "fert_rate", x: "region", fillOpacity: 0.5 })
    ),
    Plot.lineY(
      countries,
      Plot.groupX({ y: "max", sort: ([{ region }]) => ["Oceania", "Africa", "Americas", "Asia", "Europe"].indexOf(region) }, { y: "fert_rate", x: "region", strokeWidth: 10, strokeDasharray: "1", strokeLinecap: "butt" })
    )
  ]
})