Add: [Script] Basic information about loaded NewGRFs for scripts. (#9464)

Currently, scripts use various heuristics to detect loaded NewGRFs that are inherently unreliable.
The list of loaded NewGRFs is easily accessible to a human player, and thus giving
scripts the same information is consistent with the current approach to not give scripts
more information than a human player.

src/script/api/CMakeLists.txt

@@ -179,6 +179,7 @@ add_files(
     script_log.hpp
     script_map.hpp
     script_marine.hpp
+    script_newgrf.hpp
     script_news.hpp
     script_object.hpp
     script_order.hpp
@@ -246,6 +247,7 @@ add_files(
     script_log.cpp
     script_map.cpp
     script_marine.cpp
+    script_newgrf.cpp
     script_news.cpp
     script_object.cpp
     script_order.cpp