Accumulate charge instead of energy in BatteryStatsImpl

Track battery voltage along side the measured energy to calculate
battery charge consumption per EnergyConsumer. This better represents
a consumer's impact on battery. Also change numerous variable/method
names from energy units to charge units.

Bug: 180079165
Fixes: 173765509
Test: atest FrameworksCoreTests:com.android.internal.power.MeasuredEnergyStatsTest
Test: atest FrameworksCoreTests:com.android.internal.os.BatteryStatsNoteTest
Test: atest ScreenPowerCalculatorTest
Test: atest FrameworksServicesTests:com.android.server.am.MeasuredEnergySnapshotTest

Change-Id: I5e727cebf1252cc7b1645a53282de2281c68ae85