Core/AI: Make critters flee as soon as engaged in combat and make them evade after they stop running in fear

Port From (https://github.com/TrinityCore/TrinityCore/commit/934c320d4b0da40691be7449f860447fe79b4083)

Source/Game/AI/CoreAI/PassiveAI.cs

@@ -119,12 +119,18 @@ namespace Game.AI
             me.SetReactState(ReactStates.Passive);
         }
 
-        public override void DamageTaken(Unit done_by, ref uint damage)
+        public override void JustEngagedWith(Unit who)
         {
             if (!me.HasUnitState(UnitState.Fleeing))
                 me.SetControlled(true, UnitState.Fleeing);
         }
 
+        public override void OnMovementGeneratorFinalized(MovementGeneratorType type)
+        {
+            if (type == MovementGeneratorType.TimedFleeing)
+                EnterEvadeMode(EvadeReason.Other);
+        }
+
         public override void EnterEvadeMode(EvadeReason why)
         {
             if (me.HasUnitState(UnitState.Fleeing))

Source/Game/AI/CoreAI/UnitAI.cs

@@ -502,6 +502,8 @@ namespace Game.AI
         /// </summary>
         public virtual void OnGameEvent(bool start, ushort eventId) { }
 
+        public virtual void OnMovementGeneratorFinalized(MovementGeneratorType type) { }
+
         public virtual string GetDebugInfo()
         {
             return $"Me: {(me != null ? me.GetDebugInfo() : "NULL")}";