pgsql: Fix exception safety bug in typcache.c.

Fix exception safety bug in typcache.c.

If an out-of-memory error was thrown at an unfortunate time,
ensure_record_cache_typmod_slot_exists() could leak memory and leave
behind a global state that produced an infinite loop on the next call.

Fix by merging RecordCacheArray and RecordIdentifierArray into a single
array. With only one allocation or re-allocation, there is no
intermediate state.

Back-patch to all supported releases.

Reported-by: "James Pang (chaolpan)" <chaolpan(at)cisco(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/PH0PR11MB519113E738814BDDA702EDADD6EFA%40PH0PR11MB5191.namprd11.prod.outlook.com

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f899c7f1eae43a95ae5d221e754283d8fcfe8bc1

Modified Files
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src/backend/utils/cache/typcache.c | 48 +++++++++++++++++++++-----------------
src/tools/pgindent/typedefs.list | 1 +
2 files changed, 28 insertions(+), 21 deletions(-)