Mourners gathered in the Qatari capital Doha on Friday to hold funeral prayers for slain Hamas leader Ismail Haniyeh as Iran and its regional allies vowed to retaliate against Israel. With the bodies of Haniyeh and his bodyguard in coffins draped with Palestinian flags, men knelt and prayed while senior leaders of Hamas’ Qatar-based political office paid their respects to Haniyeh’s family. That included two men seen as his possible successors: Khalil al-Hayya, a Hamas senior official, and former Hamas chief Khaled Mashaal, a close Haniyeh aide. The head of the Palestinian Islamic Jihad also at…