CANNES, France — Beneath intermittent rainy skies, the Cannes Film Festival opened Tuesday with the presentation of an honorary Palme d’Or for Meryl Streep and the unveiling of Greta Gerwig’s jury, as the French Riviera spectacular kicked off a potentially volatile 77th edition. A 10-day stream of stars began flowing down the Cannes’ red carpet with the opening night film, …