INotificationOverlay
Also fixes `HasOngoingOperations` not actually working.
FillFlow.Spacing
IsDisplayingToasts
IsPresent
The reference counting was to guarantee performance (zero allocations) when the notification overlay was not required, but adds extra complexity. Instead, the toast tray now uses its ongoing height calculation as a metric for presence.
AlwaysPresent
ProgressUpdate
Remove
RemoveInternal
I'm not sure how the read status will play out going forward so I'm just adding this to keep things conforming for now.