California voters are set to decide whether to slap a new tax on the state's billionaires as IRS data show thousands of taxpayers, and billions of dollars in income, are already flowing out of the Golden State.The outflow is adding fuel to the debate over California's proposed billionaire tax, with Mark Cuban warning Saturday the measure could drive not only wealthy residents but investment and startups out of the state.Cuban's warning came amid a heated back-and-forth with Democratic Rep. Ro Khanna, who has defended the proposed tax. The billionaire investor threatened to steer future investm...