Two companies competing to develop a resort-style casino in Springfield turned in detailed plans to the city Thursday and submitted initial applications to the Massachusetts Gaming Commission. The filings by MGM Resorts International and Penn National Gaming satisfy two key deadlines as they vie with Mohegan Sun for the sole casino license allocated to Western Massachusetts. Las Vegas-based MGM delivered 18 copies of a 700-page response to Springfield’s request for extensive information about its casino plan. The company, which has proposed a more than $800 million gambling, hotel, and entertainment complex in a 10-block downtown area, promised to create more than 3,000 permanent jobs and 2,000 construction jobs. Penn National Gaming submitted the required 18 copies of its plan to the procurement office at City Hall on Thursday, the Republican newspaper of Springfield reported.