By Nichola Groom, Cole Horton and Simon Jessop LOS ANGELES/NEW YORK (Reuters) – For the first time, investors seeking to pour cash into U.S. clean energy projects can count on at least a decade of generous federal subsidies, offering them long-sought confidence in the staying power of the world’s third biggest renewables market. Tax credits for wind and solar projects have underpinned explosive growth in U.S. installations over the last decade. But they have often had short time horizons, leaving project developers scrambling to meet looming deadlines and spooking risk-averse investors. The lo…