WASHINGTON — U.S. companies would no longer be able to bar employees from taking jobs with competitors under a rule approved by a federal agency Tuesday, though the rule is sure to be challenged in court.The Federal Trade Commission voted Tuesday to ban measures known as noncompete agreements, which bar workers from jumping to or starting competing companies for a prescribed period of time. According to the FTC, 30 million people — roughly one in five workers — are now subject to such restrictions.The …