pgsql: Enable hash partitioning of text arrays

Enable hash partitioning of text arrays

hash_array_extended() needs to pass PG_GET_COLLATION() to the hash
function of the element type. Otherwise, the hash function of a
collation-aware data type such as text will error out, since the
introduction of nondeterministic collation made hash functions require
a collation, too.

The consequence of this is that before this change, hash partitioning
using an array over text in the partition key would not work.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://www.postgresql.org/message-id/flat/32c1fdae-95c6-5dc6-058a-a90330a3b621%40enterprisedb.com

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/82d4a2a7d63e79f6a6724f366cfaa4beed6b8326

Modified Files
--------------
src/backend/utils/adt/arrayfuncs.c | 2 +-
src/test/regress/expected/collate.icu.utf8.out | 50 ++++++++++++++++++++++++++
src/test/regress/sql/collate.icu.utf8.sql | 26 ++++++++++++++
3 files changed, 77 insertions(+), 1 deletion(-)