[Windows] Handle Japanese and Korean path separators

As stated in Security Considerations for Character Sets in File Names:

Windows code page and OEM character sets used on Japanese-language systems contain the Yen symbol (¥) instead of a backslash (). Thus, the Yen character is a prohibited character for NTFS and FAT file systems. When mapping Unicode to a Japanese-language code page, conversion functions map both backslash (U+005C) and the normal Unicode Yen symbol (U+00A5) to this same character. For security reasons, your applications should not typically allow the character U+00A5 in a Unicode string that might be converted for use as a FAT file name.

So it appears that the path separator is no more a backslash but some concurreny symbol. This may have bad repercussions on the code. But we will check it only after NXDRIVE-1341 is done.