Add Callback to wake up from Dream when DreamActivity is destroyed.

When a DreamActivity is destroyed, the devices remains in a dream state.
This makes it look like the DreamActivity is stuck in the background but
it is actually destroyed and DreamService does not allow another Dream
to take its place.

Bug: 242368903
Bug: 241569844
Test: Manually tested by checking that when a DreamActivity is destroyed
the device wakes up from dreaming.

Change-Id: Idcb38f2332f3a8dea0add78a4ca506877aeca8f7