vfs_real: Forward declare IOFile

Eliminates the need to rebuild some source files if the file_util header
ever changes. This also uncovered some indirect inclusions, which have
also been fixed.

src/core/file_sys/xts_archive.cpp

@@ -10,6 +10,7 @@
 #include <mbedtls/md.h>
 #include <mbedtls/sha256.h>
 #include "common/assert.h"
+#include "common/file_util.h"
 #include "common/hex_util.h"
 #include "common/logging/log.h"
 #include "core/crypto/aes_util.h"