By Alex Prewitt With his win in Beijing, the Alaskan-born star continues a tradition of U.S. dominance since the event’s Olympic debut in Sochi—and he’s doing so in style. ZHANGJIAKOU, China — The Instagram biography of Alex Hall lists his location as, simply, “Modern Art Museum,” which is fitting because the U.S. freestyle skier turned the slopestyle course here into a flipping, twisting, soaring solo installation on Wednesday morning. “He really just stays true to what he thinks is cool,” U.S. teammate Colby Stevenson gushes after Hall’s 90.01-point first run in the final held up for the gol…