When the secretive national security adviser of the United Arab Emirates, Sheikh Tahnoon bin Zayed, visited the White House in June, his American counterpart, Jake Sullivan, raised a delicate issue: G42, an artificial intelligence firm controlled by the sheikh that American officials believe is hiding the extent of its work with China. In public, the company has announced its staggering growth with a steady cadence of news releases. They have included agreements with European pharmaceutical giants like AstraZeneca and a $100 million deal with a Silicon Valley firm to build…