pgsql: Add more tests for partition tuple routing with droppedattribut

Add more tests for partition tuple routing with dropped attributes

As bug #15733 has proved, we are lacking coverage for partition tuple
routing with dropped attributes when involving three levels of
partitioning or more.  There was only an active bug in this area for
v11, and HEAD is proving to handle those scenarios fine, still it lacked
some coverage for the previous problem.

Author: Amit Langote, Michael Paquier
Discussion: https://postgr.es/m/15733-7692379e310b80ec@postgresql.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/964bae4d8456e5406753027fa5a70181ddb4c835

Modified Files
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src/test/regress/expected/insert.out | 41 ++++++++++++++++++++++++++++++++++++
src/test/regress/sql/insert.sql      | 28 ++++++++++++++++++++++++
2 files changed, 69 insertions(+)