Venture firm Andreessen Horowitz is set to lead a funding round for the startup Flock Safety, a prominent maker of license plate-reading cameras, valuing the company at about $7.5 billion, according to people familiar with the matter. The startup plans to raise about $250 million in the round, said one of the people, all of whom asked not to be identified discussing private information. The person cautioned that the details of the deal could still change....