Exxon Mobil Corp. plans to spend about $20 billion on refineries, petrochemical plants and other projects in and around the Gulf of Mexico, Chief Executive Darren Woods said Monday, underscoring how the giants of the global energy industry are turning to America. Mr. Woods outlined the 11-project spending plan, largely aimed at creating new outlets for U.S. natural gas, in a speech at the annual CERAWeek conference. It came…