By JOE McDONALD, AP Business Writer BEIJING (AP) — Struggling under U.S. sanctions, Huawei unveiled a folding smartphone with an 8-inch-wide screen Monday to show off its tech prowess but said it will be sold only in China. The Mate X2 highlights the challenges for Huawei Technologies Ltd. after Washington cut off access to U.S. processor chips and Google services. Last year, Huawei fell from the top-selling