AriaLive component in Toast should support root slot

[ling1726]

Currently the AriaLive component does not support a root slot, which makes its usage awkward with our Slot types, since event the UnknownSlotProps type needs some kind of root to exist on a component.

An easy workaround would be to pick a convention where the aria-live="polite" div can be the root slot. It's not urgent until we ever decide to make the AriaLive component public