Adding enableNightMode flag to BatterySaverPolicy.

Also migrating UiModeManagerService to register a LowPowerModeListener
so it uses the more standard interface for Battery Saver.

Bug: 119261320
Bug: 122968431
Test: atest com.android.server.power.batterysaver.BatterySaverPolicyTest
Change-Id: I669737d5985d0b2835740a53695526a2119cdf49
5 files changed