Hong Kong CNN  —  A summit of leaders from the BRICS group of major emerging economies kicks off in Brazil Sunday – but without the top leader of its most powerful member. For the first time in more than one decade of rule, Chinese leader Xi Jinping – who has made BRICS a centerpiece of his push to reshape the global balance of power – will not attend the annual leaders’ gathering. Xi’s absence from the two-day summit in Rio de Janeiro comes at a critical moment for BRICS, which owes its