Plot.initialize

A debugging routine, e.g.,

function Plot_initialize(data, {transform, ...channels} = {}) {
  data = arrayify(data);
  let index = data == null ? undefined : Uint32Array.from(data, (d, i) => i);
  if (transform !== undefined) {
    ({facets: index, data} = transform(data, [index]));
    if (index.length) ([index] = index);
  }
  return {
    data,
    index,
    ...Object.fromEntries(
      Object.entries(channels)
        .map(([name, value]) => [name, Plot.valueof(data, value)])
    )
  };
}

The issue provides a JavaScript example for a Plot_initialize debugging routine, but names no implementation file, test, entry point, or acceptance criteria. First clarify whether this is intended as a feature and what behavior should be considered complete before locating the relevant initialization code and tests.