Core/Units: add new functionality for units to block or enable combat interactions

Port From (https://github.com/TrinityCore/TrinityCore/commit/2819951dce545438724719836e3a13d3039b8690)

Source/Game/Entities/Unit/Unit.Fields.cs

@@ -55,6 +55,7 @@ namespace Game.Entities
         uint[] m_baseAttackSpeed = new uint[(int)WeaponAttackType.Max];
         internal float[] m_modAttackSpeedPct = new float[(int)WeaponAttackType.Max];
         protected uint[] m_attackTimer = new uint[(int)WeaponAttackType.Max];
+        bool _isIgnoringCombat;
 
         // Threat+combat management
         CombatManager m_combatManager;