PALMYRA, SYRIA — Experts are returning to Syria’s war-ravaged heritage sites, hoping to lay the groundwork for restoring them and reviving tourism, which they say could provide a much-needed boost to the country’s decimated economy after nearly 14 years of war. Once-thriving landmarks like the ancient city of Palmyra and the medieval Crusader castle of Crac des Chevaliers remain scarred by years of conflict, but local …