SPRINGFIELD — A dispute over a police officer’s firing contained such a thorny fact-pattern that even the state’s top judges said it was hard to digest.“This case has a complicated history, so we will set forth the facts in some detail,” Justice Robert R. Thomas cautioned in the 23-page opinion Friday.But despite its complexity, the Illinois Supreme Court relied on one of the most fundamental legal rules to resolve the case.The high court ruled an officer who participated in a board hearing …