pgsql: Add a regression test to verify that NLS translation works.

Add a regression test to verify that NLS translation works.

We've never actually had a formal test for this facility.
It seems worth adding one now, mainly because we are starting
to depend on gettext() being able to handle the PRI* macros
from <inttypes.h>, and it's not all that certain that that
works everywhere. So the test goes to a bit of effort to
check all the PRI* macros we are likely to use.

(This effort has indeed found one problem already, now fixed
in commit f8715ec86.)

Discussion: https://postgr.es/m/3098752.1765221796@sss.pgh.pa.us
Discussion: https://postgr.es/m/292844.1765315339@sss.pgh.pa.us

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/8c498479d70f963533d57d8bb1b3a58e00fe0d03

Modified Files
--------------
src/test/regress/expected/nls.out | 35 ++++++++
src/test/regress/expected/nls_1.out | 20 +++++
src/test/regress/meson.build | 2 +
src/test/regress/nls.mk | 5 ++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/po/LINGUAS | 1 +
src/test/regress/po/es.po | 159 ++++++++++++++++++++++++++++++++++++
src/test/regress/po/meson.build | 3 +
src/test/regress/regress.c | 77 +++++++++++++++++
src/test/regress/sql/nls.sql | 19 +++++
10 files changed, 322 insertions(+), 1 deletion(-)