void adw_toast_overlay_add_toast ( AdwToastOverlay* self, AdwToast* toast )
Only one toast can be shown at a time; if a toast is already being displayed,
toast or the original toast will be placed in a queue, depending on
the priority of
If called on a toast that’s already displayed, its timeout will be reset.
If called on a toast currently in the queue, the toast will be bumped forward to be shown as soon as possible.
The instance takes ownership of the data, and is responsible for freeing it.