By Dhara Ranasinghe and Stefano Rebaudo LONDON (Reuters) – The European Central Bank’s plans to dial back stimulus have been upended by Russia’s invasion of Ukraine. Policymakers meeting on Thursday must now grapple with the prospect of inflation, already at record highs, rising yet further just as a new crisis threatens the economy. “Of all the major central banks, the ECB has the biggest dilemma on its hands,” Principal Global Investors chief strategist Seema Shah said. Here are five key questions for markets. 1. What will the ECB do this week? Policy decisions remain wide open and subject t…