Frank Rizzo In “A Crossing,” the new dance musical premiering at Barrington Stage in the Berkshires, a group of desperate immigrants confront hazardous terrains, punishing weather, threatening vigilantes — and their own mixed feelings of hope, loss and doubt — as they seek safety and a better life across the U.S.-Mexican border.Directed with a graceful naturalism by Joshua Bergasse and co-choreographed with Alberto Lopez with energy, heart and authenticity, it’s a journey whose stories and