At a time when some opera companies are struggling just to maintain the status quo, the Wolf Trap Opera has considerably expanded its reach. Not only is it offering opera at the Barns at Wolf Trap, but it also has extended its collaborations so that its singers appear around the city — at the Phillips Collection, at Union Market, in College Park. Furthermore, it has brought opera back to the Filene Center: A return that began a few years ago as a semi-staged concert performance has blossomed, on Friday night, into a full production of “Rigoletto.”