The developers of two prominent downtown Baltimore apartment projects will be among the key beneficiaries of Mayor Stephanie Rawlings-Blake’s expanded tax incentive plan for apartment development. Questar Properties Inc.’s proposal for a high-rise apartment tower at 414 Light St. and the Abell Foundation’s effort to redevelop the former University of Maryland Specialty Hospital at 601 S. Charles St. are both outside of two tax incentive zones the city had offered developers. But Rawlings-Blake’s…