Lua on each mapgen thread (#13092)

src/script/lua_api/l_server.h

@@ -118,6 +118,9 @@ class ModApiServer : public ModApiBase
 	// register_async_dofile(path)
 	static int l_register_async_dofile(lua_State *L);
 
+	// register_mapgen_script(path)
+	static int l_register_mapgen_script(lua_State *L);
+
 	// serialize_roundtrip(obj)
 	static int l_serialize_roundtrip(lua_State *L);