Move over Hadid sisters, you’re no longer the only ones with upfront assets to flash. As evidenced by recent splashy, sexy looks sported by Harry Styles, a number of preening professional athletes and models at recent fashion shows, male cleavage is busting out on the studliest stars. Shirts unbuttoned to the sternum and undone jackets allow well-built men to show off nicely sculpted chest muscles. And women in the rag trade are not complaining. “I am absolutely into it,” gushes stylist Calyann Barnett, who dresses elite athletes such as Usain Bolt, Rajon Rondo and Victor Oladipo. “When you decide to...