select start (or end) point of an interval, rather than its midpoint?

there should be a way to select the start point rather than midpoint of an interval? In particular when creating a lineY with missing days, we might still want the day to be shown at 00:00 rather than 12:00.

Plot.lineY({ length: 3 }, {
    x: ["2022-11-20T00:00:00.000Z", "2022-11-21T00:00:00.000Z", "2022-11-24T00:00:00.000Z"],
    interval: d3.utcDay
  }).initialize().channels.x.value

currently this returns dates as 2022-11-20T12:00:00.000Z, etc.

Reported by @yurivish (with this concrete use case).

See also #1182

Start by tracing how Plot.lineY handles the interval option, using the provided d3.utcDay example and the linked missing-data use case. The work is done when callers can select an interval’s start or end point and the example places missing days at 00:00 rather than the midpoint.