LONDON — “Europe! Europe!” was the chant ringing out from the banks of the Danube after an election landslide that was celebrated across the continent as a stunning defeat for those threatening its security. Presidents, prime ministers and European Union officials hailed the end of Viktor Orbán's 16-year rule in Hungary as a return to unity and shared values in the European Union, the 27-nation bloc that he criticized and sought to undermine. Orbán, a close ally of Russia's Vladimir Putin and