non-utf8 string handling in p5_to_p6() very slow

[jdv]

I'm gonna guess the buf is resizing itself way too much as evidenced by the tons of calls to
brk and mremap.

Here's how I tripped over this:

[jdv@new-host-2 p6-agency]$ cat get.pl6
use v6;
use HTTP::Tiny:from;

my $h = HTTP::Tiny.new;

my $t1 = now;
my %response = $h.get('https://www.google.com');
$t1 = now - $t1;

my $t2 = now;
dd %response;#;
#say %response.decode('iso-8859-1');
$t2 = now - $t2;

say $t1;
say $t2;
[jdv@new-host-2 p6-agency]$

For even more time spent try fetching youtube.