printing: Do not truncate job names in GtkPrintOperation

printing: Do not truncate job names in GtkPrintOperation

We are currently truncating job names to 255 bytes, because that's the
maximum allowed length of job-name attribute in CUPS. This is a CUPS
limitation that GtkPrintOperation shouldn't need to know, and it
shouldn't affect other backends, that might have other limitations or
even no limitation at all. This has another side effect, that what you
set as GtkPrintOperation:job-name could be different to what you get if
the property is truncated, this is not documented in
gtk_print_operation_set_job_name(). So, I think the job name should be
truncated by the CUPS backend, right before setting the job-name
attribute.

https://bugzilla.gnome.org/show_bug.cgi?id=774097