Feature: Remember the last-used signal between games (#9792)

src/settings_type.h

@@ -21,6 +21,7 @@
 #include "zoom_type.h"
 #include "openttd.h"
 #include "rail_gui.h"
+#include "signal_type.h"
 
 /* Used to validate sizes of "max" value in settings. */
 const size_t MAX_SLE_UINT8 = UINT8_MAX;
@@ -146,6 +147,7 @@ struct GUISettings {
 	bool   pause_on_newgame;                 ///< whether to start new games paused or not
 	SignalGUISettings signal_gui_mode;       ///< select which signal types are shown in the signal GUI
 	SignalCycleSettings cycle_signal_types;  ///< Which signal types to cycle with the build signal tool.
+	SignalType default_signal_type;          ///< The default signal type, which is set automatically by the last signal used. Not available in Settings.
 	Year   coloured_news_year;               ///< when does newspaper become coloured?
 	bool   timetable_in_ticks;               ///< whether to show the timetable in ticks rather than days
 	bool   quick_goto;                       ///< Allow quick access to 'goto button' in vehicle orders window