TV has long been an industry based on eyeballs. Now media companies are winking more at feet. Fox Corp. is the backer of some of TV’s most-watched programs including Sunday-afternoon NFL games and “The Masked Singer.”  Earlier this week, however, it released a report touting not the number of people who see its shows, but rather the fact that ad campaigns from certain fast-food chains seen by viewers on its broadcast network drove foot traffic to restaurants by 81% over audiences who did not.