pgsql: postgres_fdw: Add more test coverage for EvalPlanQual testing.

postgres_fdw: Add more test coverage for EvalPlanQual testing.

postgres_fdw supports EvalPlanQual testing by using the infrastructure
provided by the core with the RecheckForeignScan callback routine (cf.
commits 5fc4c26db and 385f337c9), but there has been no test coverage
for that, except that recent commit 12609fbac, which fixed an issue in
commit 385f337c9, added a test case to exercise only a code path added
by that commit to the core infrastructure.  So let's add test cases to
exercise other code paths as well at this time.

Like commit 12609fbac, back-patch to all supported branches.

Reported-by: Masahiko Sawada <sawada.mshk@gmail.com>
Author: Etsuro Fujita <etsuro.fujita@gmail.com>
Discussion: https://postgr.es/m/CAPmGK15%2B6H%3DkDA%3D-y3Y28OAPY7fbAdyMosVofZZ%2BNc769epVTQ%40mail.gmail.com
Backpatch-through: 13

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c3eec94fc1a02a67ee51cdd781f24f6f28ad5b36

Modified Files
--------------
contrib/postgres_fdw/expected/eval_plan_qual.out | 108 +++++++++++++++++++++--
contrib/postgres_fdw/specs/eval_plan_qual.spec   |  61 +++++++++++--
2 files changed, 155 insertions(+), 14 deletions(-)