Michael Madigan, the former speaker of the Illinois House and for decades one of the nation’s most powerful legislators, was charged with a nearly $3 million racketeering and bribery scheme Wednesday, becoming the most prominent politician swept up in a federal investigation of entrenched government corruption in the state.Madigan, 79, is charged in the 22-count indictment with racketeering conspiracy, using interstate facilities in aid of bribery, wire fraud and attempted extortion. Madigan, who resigned from the …