By Guy Faulconbridge and Felix Light LONDON (Reuters) -Russia on Tuesday paved the way for the formal annexation of swathes of Ukrainian territory, backing referendum plans in areas of Ukraine its soldiers control in a direct challenge to the West that could sharply escalate the war. After nearly seven months of war, including a critical battlefield defeat in northeastern Ukraine, Russian President Vladimir Putin is pondering his next steps. Annexation could be his answer. In what appeared to be choreographed requests, Russian-backed officials across 15% of Ukrainian territory – an area about …