JEFFERSON CITY, Mo. — When a white Ferguson police officer fatally shot a black 18-year-old nearly a year ago, the St. Louis suburb erupted in violent protests, and the nation took notice. Since then, legislators in almost every state have proposed changes to the way police interact with the public.The result: Twenty-four states have passed at least 40 new measures addressing such things as officer-worn cameras, training about racial bias, independent investigations when police use force and new limits on the flow of …