Improve legend marker truncation behavior

When legend markers are truncated, they can often times be elided down to just showing an ellipsis with nothing else. This is a waste of space and should not be shown.

In such a case, the region the user must hover-over to show a tooltip that shows the full label is just the elided text "...". This is a small target, and it would be better if the tooltip would show over a larger area.

Better control over when truncation occurs is also desired.