Change indexes into tile arrays to be stored as bytes to save memory.

The index value needs only be big enough to handle all defined terrain types. This is a low number so we can save memory by defining it as a byte. This particularly saves memory for the CustomTerrain field in the Map class, which defines a cell layer for the map using tile indexes, so we can reduce the size of that layer 4x as a result.

OpenRA.Mods.RA/Bridge.cs

@@ -98,7 +98,7 @@ namespace OpenRA.Mods.RA
 				self.World.Map.CustomTerrain[c] = GetTerrainType(c);
 		}
 
-		int GetTerrainType(CPos cell)
+		byte GetTerrainType(CPos cell)
 		{
 			var dx = cell - self.Location;
 			var index = dx.X + self.World.TileSet.Templates[template].Size.X * dx.Y;