WASHINGTON/NEW YORK, June 23 (Reuters) - The U.S. Justice Department on Friday filed criminal charges against four Chinese chemical manufacturing companies and eight individuals over allegations they illegally trafficked the chemicals used to make fentanyl - a highly addictive painkiller that has fueled the opioid crisis in the United States. The indictments mark the first time the United States has sought to prosecute any of the Chinese companies responsible for manufacturing the precursor chemicals used to make the painkiller. Earlier this week, Antony Blinken made the first visit to China by a U.S. Secretary of State in five years and...