Although vaguely positioned as an Oscar-season contender thanks to its stars, its English period setting and its historical and cultural resonance, “The Imitation Game” is forever doomed to be the other 2014 film about a famous Cambridge professor. I’m not sure it’s ultimately a worse movie than the Stephen Hawking biopic “The Theory of Everything,” but it’s much closer to solid, capable British TV drama, and never makes much of a case for itself as a big-screen experience.