pgsql: Disallow partitionwise join when collations don't match

Disallow partitionwise join when collations don't match

If the collation of any join key column doesn’t match the collation of
the corresponding partition key, partitionwise joins can yield incorrect
results. For example, rows that would match under the join key collation
might be located in different partitions due to the partitioning
collation. In such cases, a partitionwise join would yield different
results from a non-partitionwise join, so disallow it in such cases.

Reported-by: Tender Wang <tndrwang(at)gmail(dot)com>
Author: Jian He <jian(dot)universality(at)gmail(dot)com>
Reviewed-by: Tender Wang <tndrwang(at)gmail(dot)com>
Reviewed-by: Junwang Zhao <zhjwpku(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAHewXNno_HKiQ6PqyLYfuqDtwp7KKHZiH1J7Pqyz0nr+PS2Dwg@mail.gmail.com
Backpatch-through: 12

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9c4757491683a10f0531bd206850d15dad8cadeb

Modified Files
--------------
src/backend/optimizer/path/joinrels.c | 4 +
src/test/regress/expected/collate.icu.utf8.out | 118 +++++++++++++++++++++++++
src/test/regress/sql/collate.icu.utf8.sql | 22 +++++
3 files changed, 144 insertions(+)