pgsql: Prevent a rowtype from being included in itself via a range.

Prevent a rowtype from being included in itself via a range.

We probably should have thought of this case when ranges were added,
but we didn't.  (It's not the fault of commit eb51af71f, because
ranges didn't exist then.)

It's an old bug, so back-patch to all supported branches.

Discussion: https://postgr.es/m/7782.1577051475@sss.pgh.pa.us

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/4af2531d03930c1fa1aa7ffc9b7cda9e23d7c03a

Modified Files
--------------
src/backend/catalog/heap.c               | 9 +++++++++
src/test/regress/expected/rangetypes.out | 3 +++
src/test/regress/sql/rangetypes.sql      | 3 +++
3 files changed, 15 insertions(+)