pgsql: Tighten check for generated column in partition key expression

Tighten check for generated column in partition key expression

A generated column may end up being part of the partition key
expression, if it's specified as an expression e.g. "(<generated
column name>)" or if the partition key expression contains a whole-row
reference, even though we do not allow a generated column to be part
of partition key expression. Fix this hole.

Co-authored-by: jian he <jian(dot)universality(at)gmail(dot)com>
Co-authored-by: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/CACJufxF%3DWDGthXSAQr9thYUsfx_1_t9E6N8tE3B8EqXcVoVfQw%40mail.gmail.com

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7180d56c5609166ac9bd7203e7ac0ad50bf400ce

Modified Files
--------------
src/backend/commands/tablecmds.c | 86 ++++++++++++++++++---------------
src/test/regress/expected/generated.out | 15 ++++++
src/test/regress/sql/generated.sql | 3 ++
3 files changed, 66 insertions(+), 38 deletions(-)