non-numeric projection coordinates

[Fil]

Plot.raster(lebron_shots, {
  x: "loc_x",
  y: "loc_y",
  fill: "shot_made_flag"
}).plot({
  width: 500,
  height: 600,
  projection: {
    type: "reflect-y",
    domain: {
      type: "MultiPoint",
      coordinates: lebron_shots.map((d) => [d.loc_x, d.loc_y])
    }
  }
})

This (on the dataset at https://observablehq.com/d/d280cb30053f69a9) shows a warning that loc_x or loc_y are not numeric. But in this case, since we have a projection, there is no ambiguity (and also no way to fix the warning), so we should avoid warning. (EDIT: my mistake, it was the color scale, so in fact the message is correct.)

A secondary issue is that the projection will no be fit correctly if we don't transform the coordinates with +d.loc_x, +d.loc_y. => The issue is with geoPath(projection).bounds, which returns strings in that case. d3/d3-geo#278

A third issue is that it's tedious to create the MultiPoint, and we could maybe use the x and y channels contents instead. (Might need to split this into 2 or 3 issues; only the first can be considered as a bug, the two others would be enhancements).