pgsql: Fix incautious CTE matching in rewriteSearchAndCycle().

Fix incautious CTE matching in rewriteSearchAndCycle().

This function looks for a reference to the recursive WITH CTE,
but it checked only the CTE name not ctelevelsup, so that it could
seize on a lower CTE that happened to have the same name. This
would result in planner failures later, either weird errors such as
"could not find attribute 2 in subquery targetlist", or crashes
or assertion failures. The code also merely Assert'ed that it found
a matching entry, which is not guaranteed at all by the parser.

Per bugs #17320 and #17318 from Zhiyong Wu.
Thanks to Kyotaro Horiguchi for investigation.

Discussion: https://postgr.es/m/17320-70e37868182512ab@postgresql.org
Discussion: https://postgr.es/m/17318-2eb65a3a611d2368@postgresql.org

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/dff6c77faf0c6bcf1d407dc3ffef9e169166c714

Modified Files
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src/backend/rewrite/rewriteSearchCycle.c | 19 ++++++++++++++++---
src/test/regress/expected/with.out | 10 ++++++++++
src/test/regress/sql/with.sql | 10 ++++++++++
3 files changed, 36 insertions(+), 3 deletions(-)