pgsql: Raise error on concurrent drop of partitioned index

Raise error on concurrent drop of partitioned index

We were already raising an error for DROP INDEX CONCURRENTLY on a
partitioned table, albeit a different and confusing one:
  ERROR:  DROP INDEX CONCURRENTLY must be first action in transaction

Change that to throw a more comprehensible error:
  ERROR:  cannot drop partitioned index \"%s\" concurrently

Michael Paquier authored the test case for indexes on temporary
partitioned tables.

Backpatch to 11, where indexes on partitioned tables were added.

Reported-by: Jan Mussler <jan.mussler@zalando.de>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/16594-d2956ca909585067@postgresql.org

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f00f5e0c1129a3b3a2140df42f11ede934bb619f

Modified Files
--------------
doc/src/sgml/ref/drop_index.sgml       |  2 ++
src/backend/commands/tablecmds.c       | 11 +++++++++++
src/test/regress/expected/indexing.out | 20 ++++++++++++++++++++
src/test/regress/sql/indexing.sql      | 13 +++++++++++++
4 files changed, 46 insertions(+)