Fix HideCitusDependentObjectsOnQueriesOfPgMetaTables function

[Naisila Puka (naisila)]

There is a crash when running vanilla tests because of the citus.hide_citus_dependent_objects GUC. We turn on this GUC only for the pg vanilla tests. This GUC runs the following function HideCitusDependentObjectsOnQueriesOfPgMetaTables. This function doesn't take into account the new mergeJoinCondition. I rewrote the function such that it checks for merge join conditions as well.

Relevant PG commit: postgres/postgres@0294df2f1

The crash can be reproduced locally like the following:

SET citus.hide_citus_dependent_objects TO on;

CREATE OR REPLACE FUNCTION
    pg_catalog.is_citus_depended_object(oid,oid)
    RETURNS bool
    LANGUAGE C
    AS 'citus', $$is_citus_depended_object$$;

-- try a system catalog
MERGE INTO pg_class c
USING (SELECT 'pg_depend'::regclass AS oid) AS j
ON j.oid = c.oid
WHEN MATCHED THEN
UPDATE SET reltuples = reltuples + 1
RETURNING j.oid;

CREATE VIEW classv AS SELECT * FROM pg_class;

MERGE INTO classv c
USING pg_namespace n
ON n.oid = c.relnamespace
WHEN MATCHED AND c.oid = 'pg_depend'::regclass THEN
UPDATE SET reltuples = reltuples - 1
RETURNING c.oid;
-- crash happens here

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