Style feature to have label truncate by default

[abey79]

In some context, it would be useful to have ui.label(txt) defaults to truncate, such as we don't have to change them all for ui.add(egui::Label::new(txt).truncate(true)). Likewise, it would be nice to have a ui.label_truncated() helper (though each might be suited for different situations).

As per:

• Use the ListItem style for the component list (in the Selection Panel when an entity is selected) rerun-io/rerun#4161 (comment)

[rustbasic]

Please also refer to #3900 and #4045 when working.

• Related Feature Request: providing a ui.label_truncate() function #3900
• Related providing a ui.label_trunc() and ui.label_wrap() and ui.label_rich() #4045