[Legend] Align bottom of legend to the zero axis

[mbondyra]

The legend and legend table that is longer than the chart looks a bit weird going below the chart. We instead want to align it to zero axis.

Originally posted by @gvnmagni in #2426 (comment)

[nickofthyme]

Personally, I think this is a very low priority/impact.

Even if we did do this I'm sure it would be split between people liking it and others asking why the legend height is being truncated. Then you have to question what the top condition is like to match the bottom.

Besides the axis/legend sizing logic being very complex as it is.

We could revisit this idea when/if we move towards composable legends that are entirely separate from the chart and can be common across many charts, as mentioned in #682.