Only use largest blocker instead of largest actor for projectile blocker overscan

Before this, we unconditionally used the largest OuterRadius of all actors inside a mod for overscanning of blockable projectiles.
However, in many mods the only blockable actors are 1-cell walls, and even if there are gates like in TS, they usually aren't the largest actors in terms of hit-shape.

So this measure should save a bit of performance by reducing the overscan radius of blockable projectiles, especially in mods where walls are the only blocking actors.

OpenRA.Mods.Common/Traits/BlocksProjectiles.cs

@@ -41,7 +41,7 @@ namespace OpenRA.Mods.Common.Traits
 
 		public static bool AnyBlockingActorsBetween(World world, WPos start, WPos end, WDist width, out WPos hit)
 		{
-			var actors = world.FindActorsOnLine(start, end, width);
+			var actors = world.FindBlockingActorsOnLine(start, end, width);
 			var length = (end - start).Length;
 
 			foreach (var a in actors)