Core/Spells: Implement sqrt based aoe damage diminishing

Port From (https://github.com/TrinityCore/TrinityCore/commit/42a6e0eb1afa431fc1efe7d4c5a62758fed42684)

Source/Framework/Constants/Spells/SpellConst.cs

@@ -20,6 +20,8 @@ namespace Framework.Constants
 
         public const float TrajectoryMissileSize = 3.0f;
 
+        public const int AoeDamageTargetCap = 20;
+
         public const int MaxPowersPerSpell = 5;
 
         public const uint VisualKitFood = 406;

Source/Framework/Constants/UnitConst.cs

@@ -406,7 +406,9 @@ namespace Framework.Constants
         AuraStack,
         CritChance,
         DurationPct,
-        Duration
+        Duration,
+        ParentSpellTargetCount,
+        ParentSpellTargetIndex
     }
 
     public enum CombatRating