Introduce WarheadArgs

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

OpenRA.Mods.Common/Warheads/CreateEffectWarhead.cs

@@ -11,6 +11,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.GameRules;
 using OpenRA.Mods.Common.Effects;
 using OpenRA.Mods.Common.Traits;
 using OpenRA.Primitives;
@@ -103,8 +104,9 @@ namespace OpenRA.Mods.Common.Warheads
 			return invalidHit ? ImpactTargetType.InvalidActor : ImpactTargetType.NoActor;
 		}
 
-		public override void DoImpact(Target target, Actor firedBy, IEnumerable<int> damageModifiers)
+		public override void DoImpact(Target target, WarheadArgs args)
 		{
+			var firedBy = args.SourceActor;
 			if (!target.IsValidFor(firedBy))
 				return;