Among economists, Japan is a byword, a punch line, a horror story. The boom of the late ’80s and early ’90s — during which it became popular to imagine a Japan-dominated economic future, the subject of Michael Crichton’s thriller “Rising Sun,” for instance — was followed by a spectacular stock-market crash. The Nikkei share index hit a high of 38,957 on Dec. 29, 1989. Over the next two decades, it fell 82 percent