Respect MultiBrush weights when path tiling

Allows biasing path tiling towards or away from using certain
MultiBrushes using their existing weight property. Note that the
probability of brush selection depends on multiple factors, not just
their direct weight.

OpenRA.Mods.Common/MapGenerator/TilingPath.cs

@@ -803,7 +803,10 @@ namespace OpenRA.Mods.Common.MapGenerator
 				}
 
 				Debug.Assert(candidates.Count >= 1, "TraceBack didn't find an original route");
-				var chosenSegment = candidates[random.Next(candidates.Count)];
+				var weights = candidates
+					.Select(c => c.MultiBrush.Weight)
+					.ToArray();
+				var chosenSegment = candidates[random.PickWeighted(weights)];
 				var chosenFrom = to - chosenSegment.Moves;
 				compositeBrush.MergeFrom(
 					chosenSegment.MultiBrush,