DateLine that spans 1970 places y-axis on 1970-01-01

When using "DateLine", and when some of the dates are before 1970-01-01, and others after 1970-01-01, the y-axis is placed on 1970-01-01.

For other years, the y-axis remains at the left of the chart.

I'm sure I can guess why it's like that (you probably map it to an interval value which crosses "0". But that detail should be hidden from the user. The y-axis should always be at the left edge on a DateLine plot (unless someone specifies its location).


Start by reproducing the DateLine case with dates on both sides of 1970-01-01 and inspect how the chart chooses the y-axis position. Trace the date-to-axis handling, add a regression test for dates spanning 1970, and verify that the axis stays at the left edge unless explicitly positioned.

Written by the indexing model from the issue text.