Add internal API to PowerManager which allows napping when device is

asleep.

This allows us to enter the dream directly while the device is off, instead of needing to wake the device before entering dream.

Bug: 246472225
Test: adb shell cmd dreams start-dreaming (while device asleep)
Test: atest PowerGroupTest
Change-Id: Id4634f3d5f7c3ae324f85f11a6991f0cab068a7d