Add: AI/GS Time Mode to choose between economy (default) and calendar time (#11603)

src/script/api/script_object.hpp

@@ -244,6 +244,20 @@ protected:
 	 */
 	static bool GetAllowDoCommand();
 
+	/**
+	 * Set if the script is running in calendar time or economy time mode.
+	 * Calendar time is used by OpenTTD for technology like vehicle introductions and expiration, and variable snowline. It can be sped up or slowed down by the player.
+	 * Economy time always runs at the same pace and handles things like cargo production, everything related to money, etc.
+	 * @param Calendar Should we use calendar time mode? (Set to false for economy time mode.)
+	 */
+	static void SetTimeMode(bool calendar);
+
+	/**
+	 * Check if the script is operating in calendar time mode, or in economy time mode. See SetTimeMode() for more information.
+	 * @return True if we are in calendar time mode, false if we are in economy time mode.
+	 */
+	static bool IsCalendarTimeMode();
+
 	/**
 	 * Set the current company to execute commands for or request
 	 *  information about.