Blackstone Inc. has reached an agreement to sell the Cosmopolitan casino and hotel on the Las Vegas Strip for $5.65 billion, telling investors that the sale is the company’s most profitable of a single asset ever. The deal separates ownership of the property from the hotel and casino operations, which are being sold to MGM Resorts International for about $1.6 billion. Blackstone acquired the two-tower property for about $1.8 billion seven years ago and spent an additional $500 million on upgrades.