Fix and expand battery saver stats tracking.

The STATE_CHARGING value had the BatterySaverState bits to resemble
"ON", so dumpsys would incorrectly say battery saver was on whenever the
device was plugged in. It also meant that the enabled count would
incorrectly increase whenever the device was plugged and unplugged. This
change fixes that by explicitly checking for the magic values before
incrementing the counters.

In addition, this adds more logging around adaptive battery saver stats
and removes the STATE_CHARGING magic value in favor of an explicit
PLUGGED/UNPLUGGED state to move away from the assumption that battery
saver is off whenever the device is plugged in.

Bug: 32423528
Bug: 119261320
Bug: 158581564
Test: atest com.android.server.power.batterysaver.BatterySaverPolicyTest
Test: atest com.android.server.power.batterysaver.BatterySaverStateMachineTest
Test: atest com.android.server.power.batterysaver.BatterySavingStatsTest
Test: atest com.android.server.power.PowerManagerServiceTest
Change-Id: I071d47299360a003febd5251c2515c0b55b3cfff