pgsql: Fix interference between covering indexes and partitionedtables

Fix interference between covering indexes and partitioned tables

The bug is caused due to the original IndexStmt that DefineIndex receives
being overwritten when processing the INCLUDE columns. Use separate list of
index params to propagate to child tables. Add tests covering this case.

Amit Langote and Alexander Korotkov.

Re-commit 5c6110c6a960ad6fe1b0d0fec6ae36ef4eb913f5 because it discovered a bug
fixed in c266ed31a8a3beed3533e6a78faeca78234cbd43

Discussion:
https://www.postgresql.org/message-id/CAJGNTeO%3DBguEyG8wxMpU_Vgvg3nGGzy71zUQ0RpzEn_mb0bSWA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/524054598fd300c75007f53aebd67f9ced33b7db

Modified Files
--------------
src/backend/commands/indexcmds.c       | 27 ++++++++++++++-------------
src/test/regress/expected/indexing.out | 24 ++++++++++++++++++++++++
src/test/regress/sql/indexing.sql      | 19 +++++++++++++++++++
3 files changed, 57 insertions(+), 13 deletions(-)