Indonesia’s president said in an interview that he wants to see the speedy construction of a giant sea wall around Jakarta to prevent the low-lying capital from sinking under the sea, lending renewed backing and a sense of urgency to a slow-moving and politically contested mega project.President Joko Widodo and his government are up against a tight timetable, including a forecast by experts that at the current rate, one-third of Jakarta could be submerged by 2050.The existential crisis facing…