Teach pg_dump to dump comments on RLS policy objects.

This was unaccountably omitted in the original RLS patch.
The SQL syntax is basically the same as for comments on triggers,
so crib code from dumpTrigger().

Per report from Marc Munro.  Back-patch to all supported branches.

Discussion: https://postgr.es/m/1581889298.18009.15.camel@bloodnok.com

src/bin/pg_dump/pg_dump.c

@@ -3666,6 +3666,8 @@ dumpPolicy(Archive *fout, PolicyInfo *polinfo)
 	TableInfo  *tbinfo = polinfo->poltable;
 	PQExpBuffer query;
 	PQExpBuffer delqry;
+	PQExpBuffer polprefix;
+	char	   *qtabname;
 	const char *cmd;
 	char	   *tag;
 
@@ -3723,6 +3725,9 @@ dumpPolicy(Archive *fout, PolicyInfo *polinfo)
 
 	query = createPQExpBuffer();
 	delqry = createPQExpBuffer();
+	polprefix = createPQExpBuffer();
+
+	qtabname = pg_strdup(fmtId(tbinfo->dobj.name));
 
 	appendPQExpBuffer(query, "CREATE POLICY %s", fmtId(polinfo->polname));
 
@@ -3743,6 +3748,9 @@ dumpPolicy(Archive *fout, PolicyInfo *polinfo)
 	appendPQExpBuffer(delqry, "DROP POLICY %s", fmtId(polinfo->polname));
 	appendPQExpBuffer(delqry, " ON %s;\n", fmtQualifiedDumpable(tbinfo));
 
+	appendPQExpBuffer(polprefix, "POLICY %s ON",
+					  fmtId(polinfo->polname));
+
 	tag = psprintf("%s %s", tbinfo->dobj.name, polinfo->dobj.name);
 
 	if (polinfo->dobj.dump & DUMP_COMPONENT_POLICY)
@@ -3755,9 +3763,16 @@ dumpPolicy(Archive *fout, PolicyInfo *polinfo)
 								  .createStmt = query->data,
 								  .dropStmt = delqry->data));
 
+	if (polinfo->dobj.dump & DUMP_COMPONENT_COMMENT)
+		dumpComment(fout, polprefix->data, qtabname,
+					tbinfo->dobj.namespace->dobj.name, tbinfo->rolname,
+					polinfo->dobj.catId, 0, polinfo->dobj.dumpId);
+
 	free(tag);
 	destroyPQExpBuffer(query);
 	destroyPQExpBuffer(delqry);
+	destroyPQExpBuffer(polprefix);
+	free(qtabname);
 }
 
 /*