Core/Spells: implement SMSG_MOUNT_RESULT and use it for transformed mounting cases

Port From (https://github.com/TrinityCore/TrinityCore/commit/fb0d2ed2b96c314ea144b3524195ae96878e0079)

Source/Framework/Constants/Spells/SpellConst.cs

@@ -2557,4 +2557,19 @@ namespace Framework.Constants
         WhiteHit = 0x01, // enchant shall only proc off white hits (not abilities)
         Limit60 = 0x02  // enchant effects shall be reduced past lvl 60
     }
+
+    public enum MountResult
+    {
+        InvalidMountee = 0,
+        TooFarAway = 1,
+        AlreadyMounted = 2,
+        NotMountable = 3,
+        NotYourPet = 4,
+        Other = 5,
+        Looting = 6,
+        RaceCantMount = 7,
+        Shapeshifted = 8,
+        ForcedDismount = 9,
+        Ok = 10 // never sent
+    }
 }

Source/Game/Network/Packets/SpellPackets.cs

@@ -1107,6 +1107,18 @@ namespace Game.Network.Packets
         uint LoadingScreenID;
     }
 
+    class MountResultPacket : ServerPacket
+    {
+        public MountResult() : base(ServerOpcodes.MountResult, ConnectionType.Instance) { }
+
+        public override void Write()
+        {
+            _worldPacket.WriteUInt32(Result);
+        }
+
+        public uint Result;
+    }
+    
     //Structs
     public struct SpellLogPowerData
     {

Source/Game/Spells/Spell.cs

@@ -3465,6 +3465,23 @@ namespace Game.Spells
             caster.SendPacket(packet);
         }
 
+        void SendMountResult(MountResult result)
+        {
+            if (result == MountResult.Ok)
+                return;
+
+            if (!m_caster.IsPlayer())
+                return;
+
+            Player caster = m_caster.ToPlayer();
+            if (caster.IsLoading())  // don't send mount results at loading time
+                return;
+
+            MountResultPacket packet = new MountResultPacket();
+            packet.Result = (uint)result;
+            caster.SendPacket(packet);
+        }
+
         void SendSpellStart()
         {
             if (!IsNeedSendToClient())
@@ -5264,7 +5281,10 @@ namespace Game.Spells
                                 return SpellCastResult.NoMountsAllowed;
 
                             if (m_caster.IsInDisallowedMountForm())
-                                return SpellCastResult.NotShapeshift;
+                            {
+                                SendMountResult(MountResult.Shapeshifted); // mount result gets sent before the cast result
+                                return SpellCastResult.DontReport;
+                            }
 
                             break;
                         }