pgsql: postgres_fdw: Fix deparsing of remote column names in stats impo

postgres_fdw: Fix deparsing of remote column names in stats import.

build_remattrmap() deparses a list of remote column names for a query
that retrieves attribute stats for them from the remote server.
Previously, it did so by using the array-literal syntax with each column
name individually quoted by quote_identifier(), causing the query to
fail on the remote server with a syntax error or no results when that
column name included a single quote or backslash, as quote_identifier()
doesn't escape those characters, making the query invalid or incorrect.
Fix by switching from the array-literal syntax to the ARRAY constructor
syntax with each column name individually quoted by
deparseStringLiteral().

Oversight in commit 28972b6fc.

Reported-by: Satya Narlapuram <satyanarlapuram@gmail.com>
Reported-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Author: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Reviewed-by: Alex Guo <guo.alex.hengchen@gmail.com>
Reviewed-by: Zhenwei Shang <a934172442@gmail.com>
Reviewed-by: Etsuro Fujita <etsuro.fujita@gmail.com>
Discussion: /messages/by-id/CAHg+QDc9=WtYi=JW6QUL6ASOJc6PcGPTuxoMkhnkQ7oi7j5atg@mail.gmail.com
Discussion: /messages/by-id/CAJTYsWWGhVDFjr+smdYdU-Q_TT9YMzXA4QcLCr7rizDOyrEEow@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5107398e6d5ecad96f3d1c0efcfc9aa02b9cdff9

Modified Files
--------------
contrib/postgres_fdw/expected/postgres_fdw.out | 12 ++++++++++++
contrib/postgres_fdw/postgres_fdw.c | 8 ++++----
contrib/postgres_fdw/sql/postgres_fdw.sql | 13 +++++++++++++
3 files changed, 29 insertions(+), 4 deletions(-)