javafx printing: Support Specifying Print to File in the API

Very commonly platform printing APIs allow you to redirect
the spooled output result of printing to a disk file rather than
sending it to the printer. This is mainly useful for printer
drivers that generate something like PDF. or Postscript.
Perhaps less so for printers that generate rasters.

In the original FX printing design work supporting this
was partly implemented but was pulled.
We should take another look at it.
It would likely be a property in JobSettings which if
set would be propagated to the underlying platform printing
APIs if supported, and ignored otherwise.
This could be initiated by the application programmatically.
And any changes by the user in a print dialog to specify a
file would be reflected back in that property.