ALEPPO, Syria — Aleppo’s largest square was packed with people of all ages: young men performing a folk dance, children playing, others buying ice cream, popcorn, peanuts and salted pumpkin seeds. A giant sign spelled out in colorful English letters, “I love Aleppo.” The scene in Saadallah al-Jabiri Square on a recent day was very different from what it was during nearly four years of war that wrecked Syria’s largest city: Rebel sniper fire and shelling — and a triple car bombing that killed dozens — had made it a no-go zone.