Add information about access method for partitioned relations in \dP+

Since 374c7a2290, it is possible to set a table AM on a partitioned
table.  This information was showing up already in psql with \d+, while
\dP+ provided no information.

This commit extends \dP+ to show the access method used by a partitioned
table or index, if set.

Author: Justin Pryzby
Discussion: https://postgr.es/m/ZkyivySXnbvOogZz@pryzbyj2023

src/bin/psql/describe.c

@@ -4113,7 +4113,7 @@ listPartitionedTables(const char *reltypes, const char *pattern, bool verbose)
 	PQExpBufferData title;
 	PGresult   *res;
 	printQueryOpt myopt = pset.popt;
-	bool		translate_columns[] = {false, false, false, false, false, false, false, false, false};
+	bool		translate_columns[] = {false, false, false, false, false, false, false, false, false, false};
 	const char *tabletitle;
 	bool		mixed_output = false;
 
@@ -4181,6 +4181,13 @@ listPartitionedTables(const char *reltypes, const char *pattern, bool verbose)
 
 	if (verbose)
 	{
+		/*
+		 * Table access methods were introduced in v12, and can be set on
+		 * partitioned tables since v17.
+		 */
+		appendPQExpBuffer(&buf, ",\n  am.amname as \"%s\"",
+						  gettext_noop("Access method"));
+
 		if (showNested)
 		{
 			appendPQExpBuffer(&buf,
@@ -4216,6 +4223,9 @@ listPartitionedTables(const char *reltypes, const char *pattern, bool verbose)
 
 	if (verbose)
 	{
+		appendPQExpBufferStr(&buf,
+							 "\n     LEFT JOIN pg_catalog.pg_am am ON c.relam = am.oid");
+
 		if (pset.sversion < 120000)
 		{
 			appendPQExpBufferStr(&buf,