Commonwealth Fusion Systems raised $863 million from investors including AI giant Nvidia Corp. to help complete a demonstration system and continue development of its first commercial plant that will generate electricity by harnessing the energy of the stars. Nvidia’s NVentures venture capital unit joins existing investors Khosla Ventures and Alphabet Inc.’s Google in backing the company, according to a statement Thursday. With this funding round, Devens, Massachusetts-based Commonwealth has rai...