pgsql: pg_locale.h: define case mapping limits.

pg_locale.h: define case mapping limits.

Clearly define case mapping upper bounds that cover all providers,
locales, and encodings: PG_MAX_CASEMAP_MBCHARS,
PG_MAX_CASEMAP_EXPANSION, and PG_CASEMAP_BUFSZ.

Also redefine UTF8_CASEMAP_BUFSZ to include room for a NUL for
consistency with PG_CASEMAP_BUFSZ.

Use PG_CASEMAP_BUFSZ for the static buffer in ltree/crc32.c.

Remove macros UNICODE_CASEMAP_LEN (which was redundant with
UNICODE_MAX_CASEMAP_CODEPOINTS from unicode_limits.h), and
UNICODE_CASEMAP_BUFSZ which was not as descriptive or helpful.

Suggested-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Reviewed-by: Rithvika Devisetti <devisettirithvika(at)gmail(dot)com>
Discussion: https://postgr.es/m/2cfbc37ae8deccd3825e36b7f31c391cbf8ff9b8.camel@j-davis.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/1e9b06a8e07c3bd394459e68902b79d7b55c2035

Modified Files
--------------
contrib/ltree/crc32.c | 2 +-
src/backend/utils/adt/pg_locale.c | 44 ++++++++++++++++++-----
src/common/unicode/generate-unicode_case_table.pl | 4 +--
src/include/common/unicode_limits.h | 4 +--
src/include/utils/pg_locale.h | 35 +++++++++++++-----
5 files changed, 67 insertions(+), 22 deletions(-)