Introduce debounce to filter rapidly toggling type-c ports

Type-c ports can quickly toggle between connected/disconnected
states. Introduce debounce to prevent sending spurious notifications.

Bug: 34972898
Test: notification should not be queued for a pixel-c charger not connected
to the power outlet.
Change-Id: I4aa19f9f864fe5b77e65f6a07a3184d8aba1f5fc