Vice President Mike Pence will sit down with Sheldon Adelson behind closed doors on Friday, a meeting that cements the Republican billionaire’s place as a key adviser to the new administration. Pence, who is speaking to the Republican Jewish Coalition that meets at Adelson’s hotel and casino in Las Vegas, The Venetian, will chat formally with Adelson just before he addresses the entire RJC on Friday evening, according to a source with knowledge of the meeting. Adelson, who disclosed nearly $80 million in donations to conservative groups in the 2016 cycle, is the country’s most prolific Republican donor, and he…