MFC r304703, r304755

1. _locale.h

LC_*_MASK bit shifting order was partially broken from the initial commit
time at year 2012. Only LC_COLLATE_MASK and LC_CTYPE_MASK are in the
right order.

The order here should match XLC_* from "xlocale_private.h" which, in turn,
match LC_* publicly visible order from <locale.h> which determines how
locale components are stored in the structure.
LC_*_MASK -> XLC_* translation done as "ffs(mask) - 1" in the querylocale()
and equivalent shift loop in the newlocale(), so mapped to some wrong
components (excluding two mentioned above).

Formally the fix is ABI breakage, but old code using those masks
never works properly in any case.
Only newlocale() and querylocale() are affected.

2. msgcat.c

Use current locale (f.e. set by thread). It was global locale always
previously.

PR: 211743