pgsql: Introduce t_isalnum() to replace t_isalpha() || t_isdigit() test

Introduce t_isalnum() to replace t_isalpha() || t_isdigit() tests.

ts_locale.c omitted support for "isalnum" tests, perhaps on the
grounds that there were initially no use-cases for that. However,
both ltree and pg_trgm need such tests, and we do also have one
use-case now in the core backend. The workaround of testing
isalpha and isdigit separately seems quite inefficient, especially
when dealing with multibyte characters; so let's fill in the
missing support.

Discussion: https://postgr.es/m/2548310.1664999615@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ca71131eebba63809ceb86be033a264a5f0a1d79

Modified Files
--------------
contrib/ltree/ltree.h | 2 +-
contrib/pg_trgm/trgm.h | 2 +-
src/backend/tsearch/ts_locale.c | 16 ++++++++++++++++
src/backend/utils/adt/tsquery.c | 2 +-
src/include/tsearch/ts_locale.h | 1 +
5 files changed, 20 insertions(+), 3 deletions(-)