WASHINGTON — The Justice Department on Thursday announced a sweeping antitrust lawsuit against Apple, accusing the tech giant of engineering an illegal monopoly in smartphones that boxes out competitors, stifles innovation and keeps prices artificially high.The lawsuit, filed in federal court in New Jersey, alleges that Apple has monopoly power in the smartphone market and leverages control over the iPhone to “engage in a broad, sustained, and illegal course of conduct.”“Apple has locked its …