Remove the various Current pointers, they are implementation internals
that shouldn't be leaked. Remove _CATEGORY_DEFAULT related handling and
directly pick the implemenation pointer from the C locale.
Merge the C locale data into global_locale.c with the exception of
_DefaultRuneLocale. Mark that one hidden. Move _RUNE_LOCALE and
_CITRUS_CTYPE into multibyte.h and pick up the correct rl_citrus_ctype
for non-default locales.
2933c53464