Introduce WarheadArgs

- Passes additional arguments to warheads on impact
- Uses that to reduce parameter count of DoImpact by 1

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -14,6 +14,7 @@ using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using OpenRA.Activities;
 using OpenRA.FileSystem;
+using OpenRA.GameRules;
 using OpenRA.Graphics;
 using OpenRA.Network;
 using OpenRA.Primitives;
@@ -490,7 +491,7 @@ namespace OpenRA.Traits
 		int Delay { get; }
 		bool IsValidAgainst(Actor victim, Actor firedBy);
 		bool IsValidAgainst(FrozenActor victim, Actor firedBy);
-		void DoImpact(Target target, Actor firedBy, IEnumerable<int> damageModifiers);
+		void DoImpact(Target target, WarheadArgs args);
 	}
 
 	public interface IRulesetLoaded<TInfo> { void RulesetLoaded(Ruleset rules, TInfo info); }