Add event PlayerConnectionConfirmed (#6274)

core/src/mindustry/game/EventType.java

@@ -480,7 +480,19 @@ public class EventType{
         }
     }
 
-    /** Called after connecting; when a player receives world data and is ready to play.*/
+    /**
+     * Called after player confirmed it has received world data and is ready to play.
+     * Note that if this is the first world receival, then player.con.hasConnected is false.
+     */
+    public static class PlayerConnectionConfirmed{
+        public final Player player;
+
+        public PlayerConnectionConfirmed(Player player){
+            this.player = player;
+        }
+    }
+
+    /** Called after connecting; when a player receives world data and is ready to play. Fired only once, after initial connection. */
     public static class PlayerJoin{
         public final Player player;