Core/Scripts: Adding script hooks to allow for third party scripts to modify damage dealt.

Originally from the VAS Autobalance script, slightly modified.

Only addresses Spells, Dots, and Melee Damage. I'll have look at the current modules on ways of doing this but, Environmental Damage(fire/lava/drowning), Fall Damage, and Potentially AoE aren't covered by these.

Closes #7867

Signed-off-by: Nay <dnpd.dd@gmail.com>

src/server/game/Scripting/ScriptMgr.h

@@ -392,7 +392,24 @@ class ItemScript : public ScriptObject
         virtual bool OnExpire(Player* /*player*/, ItemTemplate const* /*proto*/) { return false; }
 };
 
-class CreatureScript : public ScriptObject, public UpdatableScript<Creature>
+class UnitScript : public ScriptObject
+{
+    protected:
+
+        UnitScript(const char* name);
+
+    public:
+        // Called when DoT's Tick Damage is being Dealt
+        virtual void ModifyPeriodicDamageAurasTick(Unit* /*target*/, Unit* /*attacker*/, uint32& /*damage*/) { }
+
+        // Called when Melee Damage is being Dealt
+        virtual void ModifyMeleeDamage(Unit* /*target*/, Unit* /*attacker*/, uint32& /*damage*/) { }
+
+        // Called when Spell Damage is being Dealt
+        virtual void ModifySpellDamageTaken(Unit* /*target*/, Unit* /*attacker*/, int32& /*damage*/) { }
+};
+
+class CreatureScript : public UnitScript, public UpdatableScript<Creature>
 {
     protected:
 
@@ -583,7 +600,7 @@ class ConditionScript : public ScriptObject
         virtual bool OnConditionCheck(Condition* /*condition*/, ConditionSourceInfo& /*sourceInfo*/) { return true; }
 };
 
-class VehicleScript : public ScriptObject
+class VehicleScript : public UnitScript
 {
     protected:
 
@@ -654,7 +671,7 @@ class AchievementCriteriaScript : public ScriptObject
         virtual bool OnCheck(Player* source, Unit* target) = 0;
 };
 
-class PlayerScript : public ScriptObject
+class PlayerScript : public UnitScript
 {
     protected:
 
@@ -1031,6 +1048,12 @@ class ScriptMgr
         void OnGroupChangeLeader(Group* group, uint64 newLeaderGuid, uint64 oldLeaderGuid);
         void OnGroupDisband(Group* group);
 
+    public: /* UnitScript */
+
+        void ModifyPeriodicDamageAurasTick(Unit* target, Unit* attacker, uint32& damage);
+        void ModifyMeleeDamage(Unit* target, Unit* attacker, uint32& damage);
+        void ModifySpellDamageTaken(Unit* target, Unit* attacker, int32& damage);
+
     public: /* Scheduled scripts */
 
         uint32 IncreaseScheduledScriptsCount() { return ++_scheduledScripts; }