Add: [Script] Function to get all rail types of an rail engine.

src/script/api/script_rail.hpp

@@ -49,6 +49,14 @@ public:
 		RAILTYPE_INVALID  = ::INVALID_RAILTYPE, ///< Invalid RailType.
 	};
 
+	/**
+	 * A bitmap with all possible rail types.
+	 */
+	enum RailTypes : int64_t {
+		/* Note: these values represent part of the in-game RailTypes enum */
+		INVALID_RAILTYPES = INT64_MAX, ///< Invalid RailTypes.
+	};
+
 	/**
 	 * A bitmap with all possible rail tracks on a tile.
 	 */