European energy firms pledged Monday to finance half the cost of a natural-gas link from Russia to Germany, lending support to a pipeline plan that is fueling tensions within the European Union. A consortium of five companies—Engie SA, OMV AG, Royal Dutch Shell PLC, Uniper SE and Wintershall Holding GmbH—said they would provide up to €4.75 billion ($5.1 billion) in long-term financing to Nord Stream 2 AG, a wholly owned…