Optional support for reference styling

[Omikhleia]

If (optional) package resilient.styles is available (from the resilient.sile collection), then when the new v2 styling paradigm lands there (PR 13), it could be interesting for labelrefs to apply the reference styles available there.

So e.g. referring to a captioned figure ("Figure 5. Some caption") would generate "fig. 5" -- or whatever the style defines -- rather than just the "5" alone.

(Opened in advance so I remember it in due time)