pgsql: Move libc-specific code from pg_locale.c into pg_locale_libc.c.

Move libc-specific code from pg_locale.c into pg_locale_libc.c.

Move implementation of pg_locale_t code for libc collations into
pg_locale_libc.c. Other locale-related code, such as
pg_perm_setlocale(), remains in pg_locale.c for now.

Discussion: https://postgr.es/m/flat/2830211e1b6e6a2e26d845780b03e125281ea17b(dot)camel(at)j-davis(dot)com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/66ac94cdc79216e85f4c9e2d445c6f025653668e

Modified Files
--------------
src/backend/utils/adt/Makefile | 1 +
src/backend/utils/adt/meson.build | 1 +
src/backend/utils/adt/pg_locale.c | 474 +------------------------------
src/backend/utils/adt/pg_locale_libc.c | 502 +++++++++++++++++++++++++++++++++
4 files changed, 514 insertions(+), 464 deletions(-)