Santa Clara University plans to build an ambitious new science, technology, engineering and math hub, backed by a record $100 million gift from Susan and John A. Sobrato, an SCU alumnus and founder of one of Silicon Valley’s largest commercial development firms. The elegant new building, outfitted with state-of-the-art laboratories and equipment, could be a game-changer for the private, 165-year-old Jesuit university whose reputation was built on the liberal arts, creating a rare opportunity to link fast-moving technical fields with the school’s long-standing commitment to ethics.