Revert "SPIGOT-264: Remove PlayerPortalEvent's handler list"

This reverts commit 9acbabc8bd.

By: Thinkofdeath <thinkofdeath@spigotmc.org>

paper-api/src/main/java/org/bukkit/event/player/PlayerPortalEvent.java

@@ -3,6 +3,7 @@ package org.bukkit.event.player;
 import org.bukkit.Location;
 import org.bukkit.TravelAgent;
 import org.bukkit.entity.Player;
+import org.bukkit.event.HandlerList;
 
 /**
  * Called when a player is about to teleport because it is in contact with a
@@ -11,6 +12,7 @@ import org.bukkit.entity.Player;
  * For other entities see {@link org.bukkit.event.entity.EntityPortalEvent}
  */
 public class PlayerPortalEvent extends PlayerTeleportEvent {
+    private static final HandlerList handlers = new HandlerList();
     protected boolean useTravelAgent = true;
     protected TravelAgent travelAgent;
 
@@ -73,4 +75,13 @@ public class PlayerPortalEvent extends PlayerTeleportEvent {
     public void setPortalTravelAgent(TravelAgent travelAgent) {
         this.travelAgent = travelAgent;
     }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
 }