Cook County voters will cast ballots next March in a Democratic primary that pits two-term incumbent Cook County State’s Attorney Anita M. Alvarez against a pair of formidable challengers.Despite backing from powerful Chicago Democrats, Alvarez faces Kimberly M. Foxx and Donna B. More in a race that’s already generated hundreds of thousands of dollars in campaign contributions.As former chief of staff to Cook County Board President Toni Preckwinkle, Foxx also has hefty political backing. More is a corporate …