Fix crash on power menu rotation, and re-render power menu onUiModeChanged.

Test: Automated tests pass. Unplug phone, turn on battery saver, open a rotateable app (like Chrome), hold power to open Global Actions. Rotate the phone -- shouldn't crash. Plug the phone in, battery saver should disable, and the power menu should re-render with a light theme.

Fixes: 129108888
Fixes: 129555054

Change-Id: If2646d5332b18ac32796ba44a86d3cc2aae18982