How much enjoyment you can milk out of the 155 minutes required to sit through Baz Luhrmann’s sprawling, teeming, and extremely silly epic Australia will depend on what you think about its most important character. Here I do not mean Nicole Kidman or Hugh Jackman, who technically headline the film — Kidman as the English noblewoman who inherits a cattle ranch in the late-1930s Outback, Jackman as the rugged Aussie known only as “the Drover” who becomes her business partner and then, inevitably, her lover. Nor do I mean the Land Down Under itself, whose picturesque topography is captured with swooping, …