By Liangping Gao and Kevin Yao BEIJING (Reuters) -China’s manufacturing activity shrank for a third straight month in December and weakened more than expected, clouding the outlook for the country’s economic recovery and raising the case for fresh stimulus measures in the new year. The government has in recent months introduced a series of policies to shore up a feeble post-pandemic recovery, which is being held back by a severe property slump, local government debt risks and soft global demand. But the world’s second-largest economy is still struggling to gain traction. The official purchasin…