GtkPrinterOptionWidget GType not released after Display destruction

[ptziegler]

As discussed in #1832

Describe the bug

When creating a new Display, the GtkPrinterOptionWidget GType introduced with 89e9775 is initalized, but not deinitialized when the display is disposed again:

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Display.java

Lines 3800 to 3804 in da081e9

	long printerOptionWidgetType = GTK.gtk_printer_option_widget_get_type();
	long printerOptionWidgetClass = OS.g_type_class_ref (printerOptionWidgetType);
	printerOptionWidgetNewProc = OS.G_OBJECT_CLASS_CONSTRUCTOR (printerOptionWidgetClass);
	OS.G_OBJECT_CLASS_SET_CONSTRUCTOR (printerOptionWidgetClass, OS.printerOptionWidgetNewProc_CALLBACK(printerOptionWidgetNewProc));
	OS.g_type_class_unref (printerOptionWidgetClass);

Environment:

1. Select the platform(s) on which the behavior is seen:

• • All OS
• • Windows
• • Linux
• • macOS