James Murdoch, heir to billionaire media magnate Rupert Murdoch, has added the biggest reported investment yet to his closely watched portfolio: a bet on the virtual-reality provider called the Void LLC. Murdoch has invested $20 million in the business, according to a person familiar with the transaction. He’s also taken a seat on the board, said the person, who asked not to be identified because the matter isn’t yet public. He joins a high-profile list of investors, including Fidelity Management, Qualcomm Ventures and Walt Disney Co.