Dummy pg_catalog.age(xid) expression

[TennyZhuang]

Tracked by #112
Tracked by #10347

Note: There are multiple functions named age:

SELECT 
n.nspname AS function_schema, 
p.proname AS function_name,
pg_get_function_arguments(p.oid) AS arguments                                                                                                               FROM pg_proc p
LEFT JOIN pg_namespace n ON p.pronamespace = n.oid 
WHERE n.nspname = 'pg_catalog' and p.proname = 'age';

 function_schema | function_name |                        arguments
-----------------+---------------+----------------------------------------------------------
 pg_catalog      | age           | xid
 pg_catalog      | age           | timestamp with time zone, timestamp with time zone
 pg_catalog      | age           | timestamp without time zone, timestamp without time zone
 pg_catalog      | age           | timestamp with time zone
 pg_catalog      | age           | timestamp without time zone

[github-actions]

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