European leaders warned Friday that Britain could become a formidable rival, just hours after a big victory by Prime Minister Boris Johnson’s conservatives all but sealed the UK’s Brexit divorce. But the EU chiefs, meeting in Brussels, also expressed relief that British voters had sent a clear message, bringing to an end the first phase of a crisis that has dogged Europe for more than three years. Led by France and Germany, EU member states said they would pursue a swift trade deal with a tight deadline of end 2020, but insisted that any new arrangement must uphold European values...