pgsql: Add pg_iswcased().

Add pg_iswcased().

True if character has multiple case forms. Will be a useful
multibyte-aware replacement for char_is_cased().

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/630706ced04e3a7a7f0070f4e8fb88f7503a1016

Modified Files
--------------
src/backend/utils/adt/pg_locale.c         | 11 +++++++++++
src/backend/utils/adt/pg_locale_builtin.c |  7 +++++++
src/backend/utils/adt/pg_locale_icu.c     |  7 +++++++
src/backend/utils/adt/pg_locale_libc.c    | 17 +++++++++++++++++
src/include/utils/pg_locale.h             |  2 ++
5 files changed, 44 insertions(+)