pgsql: Simplify code in objectaddress.c for some property graph objects

Simplify code in objectaddress.c for some property graph objects

Property graph element labels and label properties relied on a direct
systable scan when retrieving their object descriptions. These can be
simplified with get_catalog_object_by_oid(). This offers the benefit to
do a direct syscache lookup, if available.

The same logic will be used in a follow-up patch when retrieving the
object identity parts, applying the same rule across the board for these
object types.

Extracted from a larger patch by the author.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Reviewed-by: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Reviewed-by: Alex Guo <guo(dot)alex(dot)hengchen(at)gmail(dot)com>
Discussion: https://postgr.es/m/aej1DkLwhyZWmtxJ@bdtpg

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6827de95ee094f8a2cb892a40e6f154491e78496

Modified Files
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src/backend/catalog/objectaddress.c | 28 ++++++----------------------
1 file changed, 6 insertions(+), 22 deletions(-)