WASHINGTON — U.S. President Donald Trump celebrated tech billionaires for their contributions to America on Thursday only hours after a company run by one of them, Microsoft, was accused by his vice president of abusing the visa system to bring in more foreign workers. It so happens five of the six leaders he honoured are immigrants.Before the ceremony that recognized Microsoft CEO Satya Nadella, U.S. Vice President JD Vance announced at a news conference that the tech company was being suspended from a program that allows companies to apply for green cards for skilled foreign workers with H-1B visas.The crackdown…