PGPRO-5983: fix Perl tests due to changes in PostgreSQL 15devel

The standard PostgreSQL Perl modules for testing have been moved and some have
been renamed. Try to maintain both old and new modules by exporting the
enviromental variable VERSION_NUM and conditionally loading the required modules
at compile time. We cannot load these modules at runtime because they can have
INIT blocks.

Also use Perl's 'eval' function to call functions from these modules so we don't
get compilation errors due to conditionally loading modules.

The enviromental variable PG_15_PERL_MUDULES is for running tests on Windows
using MSVC because I'm not sure if it would be better to try to find and export
the variable VERSION_NUM in vcregress.pl.. It also seems to be easier to just
export the variable VERSION_NUM in Makefile on Linux instead of creating a
version check using shell commands..

Author: Marina Polyakova

Makefile

@@ -20,3 +20,8 @@ top_builddir = ../..
 include $(top_builddir)/src/Makefile.global
 include $(top_srcdir)/contrib/contrib-global.mk
 endif
+
+# Use the enviromental variable VERSION_NUM to specify which PostgreSQL Perl
+# modules to load into Perl tests at compile time (we cannot use the function
+# 'require' to load them at runtime because they can have INIT blocks).
+export VERSION_NUM

t/001_basic.pl

@@ -6,11 +6,22 @@
 
 use strict;
 use warnings;
-use PostgresNode;
-use TestLib;
 use Test::More;
 
-plan tests => 24;
+# We cannot use the function 'require' to conditionally load PostgreSQL modules
+# at runtime because they can have INIT blocks.
+
+use constant PG_15_PERL_MUDULES =>
+	((defined $ENV{VERSION_NUM} and $ENV{VERSION_NUM} >= 150000) or
+	 defined $ENV{PG_15_PERL_MUDULES});
+
+use if PG_15_PERL_MUDULES, "PostgreSQL::Test::Cluster";
+use if PG_15_PERL_MUDULES, "PostgreSQL::Test::Utils";
+
+use if (not PG_15_PERL_MUDULES), "PostgresNode";
+use if (not PG_15_PERL_MUDULES), "TestLib";
+
+plan tests => 25;
 
 my $node;
 my $res;
@@ -20,11 +31,20 @@
 # Initialize node
 # Older version of PostgresNode.pm use get_new_node function.
 # Newer use standard perl object constructor syntax
-if (PostgresNode->can('get_new_node')) {
-	$node = get_new_node('node');
-} else {
-	$node = PostgresNode->new("node");
-}
+$res = eval
+{
+	if (PG_15_PERL_MUDULES)
+	{
+		$node = PostgreSQL::Test::Cluster->new("node");
+	}
+	else
+	{
+		$node = get_new_node("node");
+	}
+	return 1;
+};
+is($res, 1, 'the node is initialized successfully');
+
 $node->init;
 $node->start;