pgsql: ICU: use UTF8-optimized case conversion API

ICU: use UTF8-optimized case conversion API

Initializes a UCaseMap object once for use across calls, and uses
UTF8-optimized APIs.

Author: Andreas Karlsson <andreas@proxel.se>
Reviewed-by: zengman <zengman@halodbtech.com>
Discussion: https://postgr.es/m/5a010b27-8ed9-4739-86fe-1562b07ba564@proxel.se

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c4ff35f10441de7dbed4e87737bca205dcca698e

Modified Files
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src/backend/utils/adt/pg_locale_icu.c | 291 +++++++++++++++++++++++-----------
src/common/unicode/case_test.c        |   2 +-
src/include/utils/pg_locale.h         |   2 +
src/tools/pgindent/typedefs.list      |   1 +
4 files changed, 202 insertions(+), 94 deletions(-)