When leaders of the United States, Japan, Germany, France, Great Britain, Italy and Canada meet in the picturesque French seaside town of Biarritz, the official reason for their gathering will be the G-7 summit. But for many of them, the focus will be on bilateral meetings with a bombastic politician boasting a peculiar mop of bright hair — not U.S. President Donald Trump, but British Prime Minister Boris Johnson, who’ll parley with his global counterparts for the first time since taking office last month.