A jury heard a child’s chilling screams to 911 dispatchers that he had been raped by an intruder and his dad was “dying on the floor” in the attempted-murder trial yesterday of the man who is accused of breaking into the father’s Cambridge home and brutally terrorizing the pair. “Dad, are you OK?” the then-11-year-old son of a Harvard employee could be heard whimpering during the Aug. 26, 2010, call to state police dispatcher Patricia Furdon from a bedroom, where his nearly decapitated father was bleeding profusely.