Belated legacy sequels are still all the rage in Hollywood, and joining the ranks of this trend is “28 Years Later,” the long-overdue sequel to director Danny Boyle’s zombie/rage-virus thriller, “28 Days Later,” and its sequel “28 Weeks Later.” While Boyle and screenwriter Alex Garland, who are reuniting for the first time in almost two decades, have teased a third film in the rage virus trilogy, one never materialized until just a few weeks ago when the surprise sequel was announced.