(Reuters) -Chinese President Xi Jinping plans to chair a symposium to boost private sector sentiment next week that will be attended by the country's business leaders including Alibaba co-founder Jack Ma, three people with knowledge of the meeting said. Xi rarely chairs symposiums about the private sector and the event underscores the numerous challenges currently facing China Inc, from the escalation in tensions with the United States under President Donald Trump to sputtering growth for the domestic economy. Many of the entrepreneurs will be from the tech sector and Xi is expected to encourage them to expand their businesses domestically...