Utility functions to pass wxWidgets pointers from Perl to C++ code.

C++ var_dir / set_var_dir() interface to access the UI resources
from the C++ code.

xs/lib/Slic3r/XS.pm

@@ -257,6 +257,13 @@ use overload
 
 sub CLONE_SKIP { 1 }
 
+package Slic3r::GUI::PresetCollection;
+use overload
+    '@{}' => sub { $_[0]->arrayref },
+    'fallback' => 1;
+
+sub CLONE_SKIP { 1 }
+
 package main;
 for my $class (qw(
         Slic3r::BridgeDetector