Add setting for whether to show rail polyline tool

src/table/settings/gui_settings.ini

@@ -1605,6 +1605,14 @@ str      = STR_CONFIG_SETTING_HIDE_DEFAULT_STOP_LOCATION
 strhelp  = STR_CONFIG_SETTING_HIDE_DEFAULT_STOP_LOCATION_HELPTEXT
 post_cb  = [](auto) { SetWindowClassesDirty(WC_VEHICLE_ORDERS); }
 
+[SDTC_BOOL]
+var      = gui.show_rail_polyline_tool
+flags    = SF_NOT_IN_SAVE | SF_NO_NETWORK_SYNC | SF_PATCH
+def      = true
+str      = STR_CONFIG_SHOW_RAIL_POLYLINE_TOOL
+strhelp  = STR_CONFIG_SHOW_RAIL_POLYLINE_TOOL_HELPTEXT
+post_cb  = [](auto) { InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_RAIL); }
+
 ; For the dedicated build we'll enable dates in logs by default.
 [SDTC_BOOL]
 ifdef    = DEDICATED