Core/Auras: implemented SPELL_AURA_MOD_HEALING_DONE_PCT_VERSUS_TARGET_HEALTH

Port From (https://github.com/TrinityCore/TrinityCore/commit/ee2ebfe87db6e43fc0ee2e27d760d656eadf9526)

Source/Framework/Constants/Spells/SpellAuraConst.cs

@@ -375,7 +375,7 @@ namespace Framework.Constants
         ModCurrencyCategoryGainPct = 351, //NYI
         Unk352 = 352,
         ModCamouflage = 353,  // Nyi
-        ModHealingDonePctVersusTargetHealth = 354,  // NYI Restoration Shaman Mastery - Mod Healing Based On Target'S Health (Less = More Healing)
+        ModHealingDonePctVersusTargetHealth = 354,  // Restoration Shaman Mastery - Mod Healing Based On Target'S Health (Less = More Healing)
         ModCastingSpeed = 355,  // NYI
         ProvideTotemCategory = 356,
         EnableBoss1UnitFrame = 357,

Source/Game/Entities/Unit/Unit.Spells.cs

@@ -533,6 +533,12 @@ namespace Game.Entities
             // Healing done percent
             DoneTotalMod *= GetTotalAuraMultiplier(AuraType.ModHealingDonePercent);
 
+            // bonus from missing health of target
+            float healthPctDiff = 100.0f - victim.GetHealthPct();
+            foreach (AuraEffect healingDonePctVsTargetHealth in GetAuraEffectsByType(AuraType.ModHealingDonePctVersusTargetHealth))
+                if (healingDonePctVsTargetHealth.IsAffectingSpell(spellProto))
+                    MathFunctions.AddPct(ref DoneTotalMod, MathFunctions.CalculatePct((float)healingDonePctVsTargetHealth.GetAmount(), healthPctDiff));
+
             return DoneTotalMod;
         }