pgsql: Don't allow partitioned index on foreign-table partitions

Don't allow partitioned index on foreign-table partitions

Creating indexes on foreign tables is already forbidden, but local
partitioned indexes (commit 8b08f7d4820f) forgot to check for them.  Add
a preliminary check to prevent wasting time.

Another school of thought says to allow the index to be created if it's
not a unique index; but it's possible to do better in the future (enable
indexing of foreign tables, somehow), so we avoid painting ourselves in
a corner by rejecting all cases, to avoid future grief (a.k.a. backward
incompatible changes).

Reported-by: Arseny Sher
Author: Amit Langote, Álvaro Herrera
Discussion: https://postgr.es/m/87sh71cakz.fsf@ars-thinkpad

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4eaa53727542c39cca71b80e8ff3e1f742d64452

Modified Files
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src/backend/tcop/utility.c                 | 38 ++++++++++++++++++++----------
src/test/regress/expected/foreign_data.out |  7 ++++++
src/test/regress/sql/foreign_data.sql      |  6 +++++
3 files changed, 39 insertions(+), 12 deletions(-)