WASHINGTON — The surge of migrants entering the United States across the southern border increasingly includes people from a surprising place: China. Despite the distances involved and the difficulties of the journey, more than 24,000 Chinese citizens have been apprehended crossing into the United States from Mexico in the past year. That is more than in the preceding 10 years combined, according to government data. They typically fly into Ecuador, where they do not need a visa. Then, like hundr