By Susan Mathew and Noel Randewich (Reuters) – Wall Street’s main stock indexes ended lower on Friday as escalating tensions in Ukraine and U.S. statements of an imminent Russian invasion prompted investors to dump risky assets in the run-up to a long weekend. The Nasdaq fell sharply, pulled lower by declines in high-growth stocks, including Apple, Amazon and Tesla. Russian-backed separatists packed civilians onto buses out of breakaway regions in east Ukraine, another development in a conflict the West believes Moscow plans to use as justification for all-out invasion of its neighbor. Russia …