Core/Creatures: Implemented extra flag to use offhand attacks

Port From (https://github.com/TrinityCore/TrinityCore/commit/2a51edc5bcebe40c114e37ef3b24da6c8f095892)

Source/Framework/Constants/CreatureConst.cs

@@ -209,9 +209,9 @@ namespace Framework.Constants
         NoTaunt = 0x100,       // Creature Is Immune To Taunt Auras And Effect Attack Me
         NoMoveFlagsUpdate = 0x200, // Creature won't update movement flags
         GhostVisibility = 0x400,       // creature will be only visible for dead players
-        Unused11 = 0x00000800,
-        Unused12 = 0x00001000,
-        Unused13 = 0x00002000,
+        UseOffhandAttack = 0x800, // creature will use offhand attacks
+        Unused12 = 0x1000,
+        Unused13 = 0x2000,
         Worldevent = 0x4000,       // Custom Flag For World Event Creatures (Left Room For Merging)
         Guard = 0x8000,       // Creature Is Guard
         Unused16 = 0x00010000,
@@ -220,21 +220,21 @@ namespace Framework.Constants
         TauntDiminish = 0x80000,       // Taunt Is A Subject To Diminishing Returns On This Creautre
         AllDiminish = 0x100000,       // Creature Is Subject To All Diminishing Returns As Player Are
         NoPlayerDamageReq = 0x200000,       // creature does not need to take player damage for kill credit
-        Unused22 = 0x00400000,
-        Unused23 = 0x00800000,
-        Unused24 = 0x01000000,
-        Unused25 = 0x02000000,
-        Unused26 = 0x04000000,
-        Unused27 = 0x08000000,
+        Unused22 = 0x400000,
+        Unused23 = 0x800000,
+        Unused24 = 0x1000000,
+        Unused25 = 0x2000000,
+        Unused26 = 0x4000000,
+        Unused27 = 0x8000000,
         DungeonBoss = 0x10000000,        // Creature Is A Dungeon Boss (Set Dynamically, Do Not Add In Db)
         IgnorePathfinding = 0x20000000,        // creature ignore pathfinding
         ImmunityKnockback = 0x40000000,        // creature is immune to knockback effects
         Unused31 = 0x80000000,
 
         // Masks
-        AllUnused = (Unused11 | Unused12 | Unused13 | Unused16 | Unused22 | Unused23 | Unused24 | Unused25 | Unused26 | Unused27 | Unused31),
+        AllUnused = (Unused12 | Unused13 | Unused16 | Unused22 | Unused23 | Unused24 | Unused25 | Unused26 | Unused27 | Unused31),
 
-        DBAllowed = (0xFFFFFFFF & ~(AllUnused | CreatureFlagsExtra.DungeonBoss))
+        DBAllowed = (0xFFFFFFFF & ~(AllUnused | DungeonBoss))
     }
 
     public enum CreatureType