fixed jd/xd/yd double-encoding UTF-8

Buggy output:

    $ p '$x={n=>uc"Станислав"};jd$x;xd$x;yd$x'
    {
       "n" : "Ð¡Ð¢ÐÐÐÐ¡ÐÐÐ"
    }
    <?xml version="1.0" encoding="utf-8"?>
    <n>Ð¡Ð¢ÐÐÐÐ¡ÐÐÐ</n>
    ---
    n: Ð¡Ð¢ÐÐÐÐ¡ÐÐÐ

The expected output:

    $ p '$x={n=>uc"Станислав"};jd$x;xd$x;yd$x'
    {
       "n" : "СТАНИСЛАВ"
    }
    <?xml version="1.0" encoding="utf-8"?>
    <n>СТАНИСЛАВ</n>
    ---
    n: СТАНИСЛАВ

The problem is that functions wrapped by jd/xd/yd do return octets, not Unicode stream, while `print` in combination with `utf8::all` treat everything as an Unicode stream.