CompaniesJuly 17 (Reuters) - Construction of U.S. solar-manufacturing plants by Chinese companies is surging, putting China in position to dominate the nascent industry, as other American factories struggle to compete despite federal subsidies.Chinese companies will have at least 20 gigawatts' worth of annual solar panel production capacity on U.S. soil within the next year, enough to serve about half the U.S. market, according to a Reuters analysis of corporate statements, government documents,...