NEW YORK — Disney is buying a large part of Fox, including its movie and television studios, for about $52.4 billion, as the home of Mickey Mouse tries to meet competition from technology companies in the entertainment business. Disney’s all-stock deal for the Murdoch family’s 21st Century Fox gives it the studios that produce the Avatar movies, “The Simpsons” and “Modern Family.” Murdoch will form a new company to keep the U.S.