pgsql: postgres_fdw: Avoid pulling up restrict infos from subqueries

postgres_fdw: Avoid pulling up restrict infos from subqueries

Semi-join joins below left/right join are deparsed as
subqueries. Thus, we can't refer to subqueries vars from upper relations.
This commit avoids pulling conditions from them.

Reported-by: Robins Tharakan <tharakan(at)gmail(dot)com>
Bug: #18852
Discussion: https://postgr.es/m/CAEP4nAzryLd3gwcUpFBAG9MWyDfMRX8ZjuyY2XXjyC_C6k%2B_Zw%40mail.gmail.com
Author: Alexander Pyhalov <a(dot)pyhalov(at)postgrespro(dot)ru>
Reviewed-by: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Backpatch-through: 17

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/023fb512755ffb64949eb6de8464c259ca70f1bd

Modified Files
--------------
contrib/postgres_fdw/expected/postgres_fdw.out | 38 ++++++++++++++++++++++++++
contrib/postgres_fdw/postgres_fdw.c | 32 ++++++++++++++++------
contrib/postgres_fdw/sql/postgres_fdw.sql | 17 ++++++++++++
3 files changed, 79 insertions(+), 8 deletions(-)