BEIJING — China has agreed that the U.N. human rights chief can visit Xinjiang after the Beijing Olympics, the South China Morning Post said, citing unidentified sources, but activists and a Western diplomat expressed doubt after years of stalled talks. Rights groups have accused China of widescale abuses against Uyghurs and other minority groups in its far western region of Xinjiang, including mass detention, torture and forced labour. The United States has accused China of genocide. Beijing denies all allegations of abuse of Uyghurs and other Turkic Muslims and has described its policies as …