Support overloaded stringification of P5 objects

In Perl 5:
package Foo; use overload '""' => sub { "foo!" };
In Perl 6:
say $foo.Str(); # gives "foo!"

lib/Inline/Perl5.pm6

@@ -670,6 +670,11 @@ class Perl5Object {
 
     method sink() { self }
 
+    method Str() {
+        my $stringify = $!perl5.call('overload::Method', self, '""');
+        return $stringify ?? $stringify(self) !! callsame;
+    }
+
     method DESTROY {
         $!perl5.sv_refcnt_dec($!ptr) if $!ptr;
         $!ptr = OpaquePointer;

t/overload.t

@@ -0,0 +1,39 @@
+#!/usr/bin/env perl6
+
+use v6;
+use Inline::Perl5;
+use Test;
+
+my $p5 = Inline::Perl5.new;
+
+$p5.run: q:heredoc/PERL5/;
+    package Foo;
+    use overload '""' => sub {
+            my ($self) = @_;
+
+            return $$self;
+        };
+
+    sub new {
+        my ($class, $str) = @_;
+        return bless \$str, $class;
+    }
+    my $foo = Foo->new("foo");
+    package Bar;
+    sub new {
+        my ($class, $str) = @_;
+        return bless \$str, $class;
+    }
+    PERL5
+
+my $foo = $p5.invoke('Foo', 'new', 'a string!');
+is("$foo", 'a string!');
+unlike("$foo", /Perl5Object\<\d+\>/);
+
+my $bar = $p5.invoke('Bar', 'new', 'a string!');
+isnt("$bar", 'a string!');
+like("$bar", /Perl5Object\<\d+\>/);
+
+done;
+
+# vim: ft=perl6