Rename module uchar-c23 to uchar-h-c23. * modules/uchar-h-c23: Renamed from modules/uchar-c23. * lib/uchar.in.h: Update. * doc/posix-headers/uchar.texi: Update. * doc/posix-functions/mbrtoc32.texi: Update. * doc/strings.texi: Update. * modules/* (Depends-on): Update. * modules/uchar-c23: New file.