Move PerlIO to perl-libs
    
    open($f, q{<:encoding(X)}, q{file}) autoloads PerlIO and PerlIO loads
    PerlIO::encoding. The same applies to <:via(), <:mmap etc.
    
    If we subpackaged them we would require each code to list the
    dependency explicitly. In general, CPAN has some PerlIO plugins where
    it needs to be done so. But there is no reliable scanner to automate
    it.