Core/Creatures: Implemented CREATURE_STATIC_FLAG_2_ALLOW_MOUNTED_COMBAT and overriding default mount from creature addon

Port From (https://github.com/TrinityCore/TrinityCore/commit/9463933eda630be97e3ab16cf66e419d2f696109)

Source/Game/Entities/Creature/Creature.Fields.cs

@@ -29,6 +29,7 @@ namespace Game.Entities
 
         bool _isMissingCanSwimFlagOutOfCombat;
 
+        uint? _defaultMountDisplayIdOverride;
         int _creatureImmunitiesId;
         uint _gossipMenuId;
         uint? _trainerId;

Source/Game/Entities/Creature/Creature.cs

@@ -283,6 +283,9 @@ namespace Game.Entities
             ApplyAllStaticFlags(m_creatureDifficulty.StaticFlags);
 
             _staticFlags.ApplyFlag(CreatureStaticFlags.NoXp, creatureInfo.CreatureType == CreatureType.Critter || IsPet() || IsTotem() || creatureInfo.FlagsExtra.HasFlag(CreatureFlagsExtra.NoXP));
+
+            // TODO: migrate these in DB
+            _staticFlags.ApplyFlag(CreatureStaticFlags2.AllowMountedCombat, GetCreatureDifficulty().TypeFlags.HasFlag(CreatureTypeFlags.AllowMountedCombat));
             _staticFlags.ApplyFlag(CreatureStaticFlags4.TreatAsRaidUnitForHelpfulSpells, GetCreatureDifficulty().TypeFlags.HasFlag(CreatureTypeFlags.TreatAsRaidUnit));
 
             return true;
@@ -1056,7 +1059,7 @@ namespace Game.Entities
         {
             base.AtEngage(target);
 
-            if (!GetCreatureDifficulty().TypeFlags.HasFlag(CreatureTypeFlags.AllowMountedCombat))
+            if (!HasFlag(CreatureStaticFlags2.AllowMountedCombat))
                 Dismount();
 
             RefreshCanSwimFlag();
@@ -2522,8 +2525,9 @@ namespace Game.Entities
             CreatureAddon creatureAddon = GetCreatureAddon();
             if (creatureAddon == null)
                 return false;
-
-            if (creatureAddon.mount != 0)
+            
+            uint mountDisplayId = _defaultMountDisplayIdOverride.GetValueOrDefault(creatureAddon.mount);
+            if ( mountDisplayId != 0)
                 Mount(creatureAddon.mount);
 
             SetStandState((UnitStandStateType)creatureAddon.standState);
@@ -3122,6 +3126,14 @@ namespace Game.Entities
                 Log.outDebug(LogFilter.Unit, $"Creature::SetCannotReachTarget() called with true. Details: {GetDebugInfo()}");
         }
 
+        void SetDefaultMount(uint? mountCreatureDisplayId)
+        {
+            if (mountCreatureDisplayId.HasValue && !CliDB.CreatureDisplayInfoStorage.HasRecord(mountCreatureDisplayId.Value))
+                mountCreatureDisplayId = null;
+
+            _defaultMountDisplayIdOverride = mountCreatureDisplayId;
+        }
+
         public float GetAggroRange(Unit target)
         {
             // Determines the aggro range for creatures (usually pets), used mainly for aggressive pet target selection.