pgsql: Fix multi-row INSERT with a sublink in a target column subscript

Fix multi-row INSERT with a sublink in a target column subscript

For INSERT ... VALUES with more than one row, transformInsertStmt()
calls transformInsertRow() once for each VALUES row and once more for
the final targetlist, and each call transformed the same raw
indirection from the target column list. That doesn't work for
sublinks, because transformSubLink() replaces the raw subselect with
its analyzed Query, so the second pass failed with "unexpected
non-SELECT command in SubLink". Other nodes that are transformed in
place, such as NullTest, failed with "unrecognized node type".

Fix by giving each transformation its own copy of the indirection.

Claude found this issue when reviewing another bug.

Discussion: https://postgr.es/m/CA+HiwqHCZLZV_20nz3fQX+1=vyFLDMbG0_3wY=QujNKZWts0nw@mail.gmail.com
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Shihao Zhong <zhong950419(at)gmail(dot)com>
Backpatch-through: 14

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/861a9c4026e6c99fbb589d20fe0b9304ef99433c

Modified Files
--------------
src/backend/parser/analyze.c | 8 +++++++-
src/test/regress/expected/insert.out | 10 ++++++++++
src/test/regress/sql/insert.sql | 4 ++++
3 files changed, 21 insertions(+), 1 deletion(-)