pgsql: Add support for Unicode case folding.

Add support for Unicode case folding.

Expand case mapping tables to include entries for case folding, which
are parsed from CaseFolding.txt.

Discussion: https://postgr.es/m/a1886ddfcd8f60cb3e905c93009b646b4cfb74c5.camel%40j-davis.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4e7f62bc386a479593e4e8ecfb94370f5a88e522

Modified Files
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src/common/unicode/Makefile                       |    6 +-
src/common/unicode/case_test.c                    |   32 +-
src/common/unicode/generate-unicode_case_table.pl |  110 +-
src/common/unicode/meson.build                    |    4 +-
src/common/unicode_case.c                         |   32 +
src/include/common/unicode_case.h                 |    3 +
src/include/common/unicode_case_table.h           | 6218 +++++++++++----------
7 files changed, 3280 insertions(+), 3125 deletions(-)