localedata: Adjust C.UTF-8 to align with C/POSIX.

localedata: Adjust C.UTF-8 to align with C/POSIX.

We have had one downstream report from Canonical [1] that
an rrdtool test was broken by the differences in LC_TIME
that we had in the non-builtin C locale (C.UTF-8). If one
application has an issue there are going to be others, and
so with this commit we review and fix all the issues that
cause the builtin C locale to be different from C.UTF-8,
which includes:
* mon_decimal_point should be empty e.g. ""
 - Depends on mon_decimal_point_wc fix.
* negative_sign should be empty e.g. ""
* week should be aligned with the builtin C/POSIX locale
* d_fmt corrected with escaped slashes e.g. "%m//%d//%y"
* yesstr and nostr should be empty e.g. ""
* country_ab2 and country_ab3 should be empty e.g. ""

We bump LC_IDENTIFICATION version and adjust the date to
indicate the change in the locale.

A new tst-c-utf8-consistency test is added to ensure
consistency between C/POSIX and C.UTF-8.

Tested on x86_64 and i686 without regression.

[1] https://sourceware.org/pipermail/libc-alpha/2022-January/135703.html

Co-authored-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Florian Weimer <fweimer@redhat.com>