BEIJING—China’s market regulator said on Friday it had fined 12 companies related to 10 deals that violated anti-monopoly rules. The companies included Baidu Inc., Tencent Holdings, Didi Chuxing, SoftBank, and a ByteDance-backed firm, the State Administration for Market Regulation (SAMR) said in a statement on Friday. The companies were fined 500,000 yuan ($77,000) each for…