Move EnumString to separate file and add enum_to_string (#15714)

src/content/mods.cpp

@@ -15,6 +15,7 @@
 #include "porting.h"
 #include "convert_json.h"
 #include "script/common/c_internal.h"
+#include "exceptions.h"
 
 void ModSpec::checkAndLog() const
 {

src/content/subgames.cpp

@@ -12,6 +12,7 @@
 #include "defaultsettings.h" // for set_default_settings
 #include "map_settings_manager.h"
 #include "util/string.h"
+#include "exceptions.h"
 
 // The maximum number of identical world names allowed
 #define MAX_WORLD_NAMES 100