LAS VEGAS — On a Sunday afternoon this month in North Las Vegas, Anna Bailey could be found at the back of the Aliante Casino, Hotel and Spa’s theater rehearsing her moves. Bailey, a dancer who has had a pioneering and historic career, had emerged from a half-century retirement to perform in a revival of “Follies.” Although you would never have guessed by watching her that the 97-year-old had not performed since the 1970s.