[meshcat] Provide better handling for truncated labels in control panel

[trowell-tri]

Long label text in the Meshcat control panel gets truncated, leaving users with no way to differentiate some labels. This has been noticed in slider labels but might also become an issue with buttons and the scene tree.

A simple solution would be to add hover text with the full label, either just for labels that are too wide or for all labels.

[trowell-tri]

See RussTedrake/manipulation#151 for a related issue.

[pathammer]

BTW there is a dat gui parameter named resizable that makes it so when you click and drag on the "open/close controls button" you resize the width of the tool. Worth trying this option in addition to hover tooltips 👍

relevant line of code: https://github.com/dataarts/dat.gui/blob/19c4725d03456ce5049e7131907fc0470326d5ae/src/dat/gui/GUI.js#L148C5-L148C14

[trowell-tri]

Thank you, I'm going to give that a try!