Expose sequence page LSN via pg_get_sequence_data.

This patch enhances the pg_get_sequence_data function to include the
page-level LSN (Log Sequence Number) of the sequence. This additional
metadata will be used by upcoming patches to support synchronization
of sequences during logical replication.

By exposing the LSN, we enable more accurate tracking of sequence
changes, which is essential for maintaining consistency across
replicated nodes.

Author: vignesh C <vignesh21@gmail.com>
Reviewed-by: shveta malik <shveta.malik@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAA4eK1LC+KJiAkSrpE_NwvNdidw9F2os7GERUeSxSKv71gXysQ@mail.gmail.com

src/test/regress/expected/sequence.out

@@ -840,10 +840,10 @@ SELECT nextval('test_seq1');
 (1 row)
 
 -- pg_get_sequence_data
-SELECT * FROM pg_get_sequence_data('test_seq1');
- last_value | is_called 
-------------+-----------
-         10 | t
+SELECT last_value, is_called, page_lsn <= pg_current_wal_lsn() as lsn FROM pg_get_sequence_data('test_seq1');
+ last_value | is_called | lsn 
+------------+-----------+-----
+         10 | t         | t
 (1 row)
 
 DROP SEQUENCE test_seq1;

src/test/regress/sql/sequence.sql

@@ -414,6 +414,6 @@ SELECT nextval('test_seq1');
 SELECT nextval('test_seq1');
 
 -- pg_get_sequence_data
-SELECT * FROM pg_get_sequence_data('test_seq1');
+SELECT last_value, is_called, page_lsn <= pg_current_wal_lsn() as lsn FROM pg_get_sequence_data('test_seq1');
 
 DROP SEQUENCE test_seq1;