Apple Inc. has expanded the job of hardware chief John Ternus to include design work, solidifying his status as a leading contender to eventually succeed Chief Executive Officer Tim Cook. Cook, who has led Apple since 2011 and turned 65 in November, quietly tapped Ternus to manage the company’s design teams at the end of last year, according to people with knowledge of the matter. That widens Ternus’ role to add one of the company’s most critical functions....