Per its title, the NBC sitcom “ The Fall and Rise of Reggie Dinkins ” is a comeback story, but it’s also a reunion. Comedian Tracy Morgan has produced a wide-ranging body of work since his breakout on “Saturday Night Live” at the turn of the millennium — and, more dramatically, since sustaining severe injuries in a New Jersey traffic collision in 2014. But his most iconic role remains, if not himself, then a part directly adjacent to his own persona: Tracy Jordan, the chaotic yet lovable co-