pgsql: hstore: Tighten key/value parsing check for whitespaces

hstore: Tighten key/value parsing check for whitespaces

isspace() can be locale-sensitive depending on the platform, causing
hstore to consider as whitespaces characters it should not see as such.
For example, U+0105, being decoded as 0xC4 0x85 in UTF-8, would be
discarded from the input given.

This problem is similar to 9ae2661, though it was missed that hstore
can also manipulate non-ASCII inputs, so replace the existing isspace()
calls with scanner_isspace().

This problem exists for a long time, so backpatch all the way down.

Author: Evan Jones
Discussion: https://postgr.es/m/CA+HWA9awUW0+RV_gO9r1ABZwGoZxPztcJxPy8vMFSTbTfi4jig@mail.gmail.com
Backpatch-through: 11

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/d522b05c8c1c2c430b2c8be795c609f6f4f2ce44

Modified Files
--------------
contrib/hstore/Makefile | 2 +-
contrib/hstore/expected/hstore_utf8.out | 36 +++++++++++++++++++++++++++++++
contrib/hstore/expected/hstore_utf8_1.out | 8 +++++++
contrib/hstore/hstore_io.c | 9 ++++----
contrib/hstore/meson.build | 1 +
contrib/hstore/sql/hstore_utf8.sql | 19 ++++++++++++++++
6 files changed, 70 insertions(+), 5 deletions(-)