Add AnimationCompletedEvent "Finished" boolean.

Content has multiple cases where AnimationCompletedEvent is used to loop an animation. #5238 broke some of these by making this event raised even when manually removed.

Luckily most cases in content tie the animation looping to the presence of a component, so the component getting removed means there's nothing to refresh the loop. LightBehavior is not as fortunate however, causing bugs like space-wizards/space-station-14#29144

This boolean allows looping code to properly distinguish the event, so it won't try to restart an animation after removing it directly.

RELEASE-NOTES.md

@@ -39,7 +39,7 @@ END TEMPLATE-->
 
 ### New features
 
-*None yet*
+* Added a `Finished` boolean to `AnimationCompletedEvent` which allows distinguishing if an animation was removed prematurely or completed naturally.
 
 ### Bugfixes
 

Robust.Client/GameObjects/EntitySystems/AnimationPlayerSystem.cs

@@ -76,7 +76,8 @@ private bool Update(EntityUid uid, AnimationPlayerComponent component, float fra
             foreach (var key in remie)
             {
                 component.PlayingAnimations.Remove(key);
-                EntityManager.EventBus.RaiseLocalEvent(uid, new AnimationCompletedEvent {Uid = uid, Key = key}, true);
+                var completedEvent = new AnimationCompletedEvent {Uid = uid, Key = key, Finished = true};
+                EntityManager.EventBus.RaiseLocalEvent(uid, completedEvent, true);
             }
 
             return false;
@@ -187,7 +188,8 @@ public void Stop(Entity<AnimationPlayerComponent?> entity, string key)
                 return;
             }
 
-            EntityManager.EventBus.RaiseLocalEvent(entity.Owner, new AnimationCompletedEvent {Uid = entity.Owner, Key = key}, true);
+            var completedEvent = new AnimationCompletedEvent {Uid = entity.Owner, Key = key, Finished = false};
+            EntityManager.EventBus.RaiseLocalEvent(entity.Owner, completedEvent, true);
         }
 
         public void Stop(EntityUid uid, AnimationPlayerComponent? component, string key)
@@ -203,5 +205,11 @@ public sealed class AnimationCompletedEvent : EntityEventArgs
     {
         public EntityUid Uid { get; init; }
         public string Key { get; init; } = string.Empty;
+
+        /// <summary>
+        /// If true, the animation finished by getting to its natural end.
+        /// If false, it was removed prematurely via <see cref="AnimationPlayerSystem.Stop(Robust.Client.GameObjects.AnimationPlayerComponent,string)"/> or similar overloads.
+        /// </summary>
+        public bool Finished { get; init; }
     }
 }