Doc: unify use of timestamp with time zone vs timestamptz

For pg_stat_all_tables, last_vacuum, last_autovacuum and co all used the
full "timestamp with time zone" type name.  For consistency, make the
newly added "last_seq_scan" also use the full type name instead of
"timestamptz".

Author: Noriyoshi Shinoda
Discussion: https://postgr.es/m/DM4PR84MB17348EA11FA90A9BE896AF89EE489%40DM4PR84MB1734.NAMPRD84.PROD.OUTLOOK.COM

doc/src/sgml/monitoring.sgml

@@ -4863,7 +4863,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>last_seq_scan</structfield> <type>timestamptz</type>
+       <structfield>last_seq_scan</structfield> <type>timestamp with time zone</type>
       </para>
       <para>
        The time of the last sequential scan on this table, based on the
@@ -4891,7 +4891,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>last_idx_scan</structfield> <type>timestamptz</type>
+       <structfield>last_idx_scan</structfield> <type>timestamp with time zone</type>
       </para>
       <para>
        The time of the last index scan on this table, based on the
@@ -5170,7 +5170,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>last_idx_scan</structfield> <type>timestamptz</type>
+       <structfield>last_idx_scan</structfield> <type>timestamp with time zone</type>
       </para>
       <para>
        The time of the last scan on this index, based on the