DETROIT — Ford, Fiat Chrysler, Honda and Toyota have taken steps to restart North American factories that have been closed to protect workers from the coronavirus. The plants would reopen in early or mid-April, restoring the largest source of cash for automakers that generally book revenue when they ship vehicles to dealerships. Auto companies, like other businesses, are trying to manage their way through the coronavirus crisis, which has forced factories to close amid employee concerns that they could catch the virus while working close to others at factory work stations.