“Leopoldstadt,” the most slow-burn and personal work of 82-year-old Tom Stoppard’s long stage and screen career, is an intimate epic. It springs to astonishing dramatic life in a now bare, but once glorious apartment off Vienna’s Ringstrasse in 1955. The only problem is, for all the visceral emotional intensity of that scene, it forms less than the last quarter of a play that begins, two hours earlier, at the same address in 1899.