pgsql: Make collation not depend on setlocale().

Make collation not depend on setlocale().

Now that the result of pg_newlocale_from_collation() is always
non-NULL, then we can move the collate_is_c and ctype_is_c flags into
pg_locale_t. That simplifies the logic in lc_collate_is_c() and
lc_ctype_is_c(), removing the dependence on setlocale().

This commit also eliminates the multi-stage initialization of the
collation cache.

As long as we have catalog access, then it's now safe to call
pg_newlocale_from_collation() without checking lc_collate_is_c()
first.

Discussion: https://postgr.es/m/cfd9eb85-c52a-4ec9-a90e-a5e4de56e57d@eisentraut.org
Reviewed-by: Peter Eisentraut, Andreas Karlsson

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/72fe6d24a38c88e112d5e63a8e907c3e96ae46ad

Modified Files
--------------
src/backend/utils/adt/pg_locale.c | 180 +++++------------------------
src/include/utils/pg_locale.h | 14 +++
src/test/regress/expected/collate.utf8.out | 26 +++++
src/test/regress/sql/collate.utf8.sql | 15 +++
4 files changed, 81 insertions(+), 154 deletions(-)