Labor Day Weekend is normally a dumping ground for the movie business, but not in 2020. Two blockbusters, "Mulan" and "Tenet," are using very different platforms to reach audiences this weekend. One is a pricey premium addition to streaming service Disney+, the other is available in whatever theaters across the country are open amid the pandemic. How each of these $200 million blockbusters does on its respective distribution platform will help shape Hollywood's next steps with its highest-profile products for months or even years to come.