Add turret-linking support to HitShape

Allows to link a HitShape to the
position and facing of a turret.

OpenRA.Mods.Common/Warheads/TargetDamageWarhead.cs

@@ -38,7 +38,7 @@ namespace OpenRA.Mods.Common.Warheads
 
 				var closestActiveShape = victim.TraitsImplementing<HitShape>()
 					.Where(Exts.IsTraitEnabled)
-					.Select(s => Pair.New(s, s.Info.Type.DistanceFromEdge(pos, victim)))
+					.Select(s => Pair.New(s, s.DistanceFromEdge(victim, pos)))
 					.MinByOrDefault(s => s.Second);
 
 				// Cannot be damaged without an active HitShape or if HitShape is outside Spread