Use Array.IndexOf to speed up Shroud.Tick.

As the `touched` cell layer uses Boolean values, Array.IndexOf is able to use a fast vectorised search. Most values in the array are false, so the search is able to significantly improve the performance of finding the next true value in the array.

OpenRA.Game/Map/ProjectedCellLayer.cs

@@ -9,6 +9,7 @@
  */
 #endregion
 
+using System;
 using OpenRA.Primitives;
 
 namespace OpenRA
@@ -53,5 +54,15 @@ namespace OpenRA
 		{
 			return Bounds.Contains(uv.U, uv.V);
 		}
+
+		public int IndexOf(T value, int startIndex)
+		{
+			return Array.IndexOf(Entries, value, startIndex);
+		}
+
+		public void SetAll(T value)
+		{
+			Array.Fill(Entries, value);
+		}
 	}
 }