BulletType despawnUnit field (#7088)

* a

* i guess so

* despawnUnitCount, which i forgot to include

core/src/mindustry/entities/bullet/BulletType.java

@@ -184,6 +184,10 @@ public class BulletType extends Content implements Cloneable{
     public Seq<BulletType> spawnBullets = new Seq<>();
     /** Unit spawned _instead of_ this bullet. Useful for missiles. */
     public @Nullable UnitType spawnUnit;
+    /** Unit spawned when this bullet hits something or despawns due to it hitting the end of its lifetime. */
+    public @Nullable UnitType despawnUnit;
+    /** Amount of units spawned when this bullet despawns. */
+    public int despawnUnitCount = 1;
 
     /** Color of trail behind bullet. */
     public Color trailColor = Pal.missileYellowBack;
@@ -443,6 +447,12 @@ public class BulletType extends Content implements Cloneable{
             createFrags(b, b.x, b.y);
         }
 
+        if(despawnUnit != null){
+            for(int i = 0; i < despawnUnitCount; i++){
+                despawnUnit.spawn(b.team, b.x + Mathf.range(0.1f), b.y);
+            }
+        }
+
         despawnEffect.at(b.x, b.y, b.rotation(), hitColor);
         despawnSound.at(b);