By Ron Bousso and Dmitry Zhdannikov LONDON (Reuters) – BP is abandoning its 19.75% stake in Russian oil giant Rosneft after Russia’s invasion of Ukraine, it said on Sunday, in an abrupt and costly end to three often fraught decades of operating in the oil-rich country. Rosneft accounts for around half of BP’s oil and gas reserves and a third of its production and divesting the stake will result in charges of up to $25 billion, the British oil and gas giant said, without saying how it plans to extricate itself. “I have been deeply shocked and saddened by the situation unfolding in Ukraine and m…