Makes @default_page_setup the default page setup for @op.
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::request-page-setup] signal.
a GtkPageSetup, or %NULL
See Implementation
Makes @default_page_setup the default page setup for @op.
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::request-page-setup] signal.