Use UTF-8 exclusively internally

This removes SystemString, SystemChar, etc.
All filepaths and log strings are assumed to be UTF-8,
with conversions to UTF-16 for Windows APIs as appropriate.

Updates amuse, athena, boo, kabufua and nod

Runtime/AutoMapper/CAutoMapper.cpp

@@ -14,6 +14,7 @@
 #include "Runtime/Particle/CGenDescription.hpp"
 #include "Runtime/World/CPlayer.hpp"
 
+#include <fmt/xchar.h>
 #include <zeus/CEulerAngles.hpp>
 
 namespace metaforce {