HARRISBURG, Pa. — Businesses that manufacture frames that can be built into working firearms sued Pennsylvania’s attorney general on Friday, five days after he issued a legal opinion classifying the products as guns under state law. The Commonwealth Court lawsuit asks a state judge to stop the state police from implementing any new policy, including background checks, based on the written opinion the agency received Monday from Democratic Attorney General Josh Shapiro. Mr. Shapiro told state police to treat unassembled “ghost guns,” gun frames also referred to as 80% receivers, as firearms.