[d3-state-visualizer] Shorten the object parts

[zalmoxisus]

When there's a lot of data, the tooltip becomes unusable, so would be nice to show at least a part of it as a preview.

Basically we'll need to shorten: when a string is long, object keys or an array length exceeds a certain value.

UPDATE: This is from d3-state-visualizer, not d3tooltip. We'll get it merged here later.