LONDON—BP is abandoning its stake in Russian oil giant Rosneft in an abrupt and costly end to three decades of operating in the energy-rich country, marking the most significant move yet by a Western company in response to Moscow’s invasion of Ukraine. Rosneft accounts for around half of BP’s oil and gas reserves and a third of its production and divesting the 19.75 percent stake will result in charges of up to $25 billion, the British company said, without saying how it plans to extricate itself. “I have been deeply shocked and saddened by the situation unfolding in Ukraine and my heart goes out to everyone affected. It has caused us to fundamentally rethink BP’s position with Rosneft,” BP Chief Executive Bernard Looney said. The rapid retreat represents a dramatic exit for BP, the biggest foreign investor in Russia, and puts the spotlight on other Western companies with operations in …