This adds specific marshallers for all of the locations where a generic
marshaller is being used. It also provides va_marshallers to reduce the
chances that we get stack traces from perf going through ffi_call_unix64.
When creating the motion controller, we know the widget that is of interest
based on gtk_event_controller_motion_new(). However, not all incoming
events are guaranteed to be of the GdkWindow associated to that widget.
They may also be for a descendant. Therefore, it is useful to translate
those coordinates into the target widget coordinate space as that is
likely what they care about.
