fit tip

[Fil]

fixes #2011

saving as draft as I don't think we have enough test coverage

[mbostock]

I made a notebook to explore the logic: https://observablehq.com/d/248a1e32c96c45db

The fitLeft check doesn’t strictly mean “the tip would fit using the left anchor” because the tip could still be outside the vertical bounds. It tells you when any of the left-anchored tips cross the right edge of the chart area.

Also I think the pointerSize is effectively doubled when using a corner anchor, which doesn’t seem right?