Makes default_page_setup the default page setup for this.
This page setup will be used by [method@Gtk.PrintOperation.run], but it can be overridden on a per-page basis by connecting to the [
signal@Gtk.PrintOperation:GtkPrintOperation:request-page-setup] signal.
| this |
a `GtkPrintOperation` |
| default_page_setup |
a `GtkPageSetup` |