What did Jay-Z and Jack Dorsey talk about when they went yachting around the Hamptons together last summer? Perhaps only Beyoncé knows. Maybe now we do, too. Square, the mobile payments company led by Mr. Dorsey, announced on Thursday its plan to acquire a “significant majority” of Tidal, the streaming music service owned by Jay-Z and other artists — including Beyoncé, Jay-Z’s wife, and Rihanna, who is a client of Jay-Z’s entertainment management company, Roc Nation.