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
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/976cb11f6c58b8807455982ae7344b72ea2cd1ab

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(+)