Core/Misc: Rename AddXXXFlag updatefield functions to SetXXXFlag

Port From (https://github.com/TrinityCore/TrinityCore/commit/b47185cabfbdeeaf492bf2303635db07ce703785)

Source/Game/Movement/Generators/ConfusedMovementGenerator.cs

@@ -43,7 +43,7 @@ namespace Game.Movement
                 return;
 
             // TODO: UNIT_FIELD_FLAGS should not be handled by generators
-            owner.AddUnitFlag(UnitFlags.Confused);
+            owner.SetUnitFlag(UnitFlags.Confused);
             owner.StopMoving();
 
             _timer.Reset(0);

Source/Game/Movement/Generators/FleeingMovementGenerator.cs

@@ -47,7 +47,7 @@ namespace Game.Movement
                 return;
 
             // TODO: UNIT_FIELD_FLAGS should not be handled by generators
-            owner.AddUnitFlag(UnitFlags.Fleeing);
+            owner.SetUnitFlag(UnitFlags.Fleeing);
             _path = null;
             SetTargetLocation(owner);
         }

Source/Game/Movement/Generators/FlightPathMovementGenerator.cs

@@ -50,7 +50,7 @@ namespace Game.Movement
             RemoveFlag(MovementGeneratorFlags.Deactivated);
 
             owner.CombatStopWithPets();
-            owner.AddUnitFlag(UnitFlags.RemoveClientControl | UnitFlags.OnTaxi);
+            owner.SetUnitFlag(UnitFlags.RemoveClientControl | UnitFlags.OnTaxi);
 
             uint end = GetPathAtMapEnd();
             uint currentNodeId = GetCurrentNode();