Add unitSpawnEvent (#5876)

core/src/mindustry/ai/WaveSpawner.java

@@ -196,6 +196,7 @@ public class WaveSpawner{
         unit.apply(StatusEffects.invincible, 60f);
         unit.add();
 
+        Events.fire(new UnitSpawnEvent(unit));
         Call.spawnEffect(unit.x, unit.y, unit.rotation, unit.type);
     }
 

core/src/mindustry/game/EventType.java

@@ -428,6 +428,15 @@ public class EventType{
         }
     }
 
+    /** Called when a unit is spawned by wave. */
+    public static class UnitSpawnEvent{
+        public final Unit unit;
+
+        public UnitSpawnEvent(Unit unit) {
+            this.unit = unit;
+        }
+    }
+
     /** Called when a unit is dumped from any payload block. */
     public static class UnitUnloadEvent{
         public final Unit unit;