Xpeng's robotics arm raised more than $900 million earlier this week at a post-money valuation above $6.3 billion. IDG Capital led the round; Gaorong Ventures, Tencent and Alibaba joined. Xpeng calls it the largest single private financing stage in the history of China's embodied AI industry — AI systems built directly into physical machines. It is also the clearest evidence yet that Chinese…