Use BatteryStats instead of BatteryStatsImpl in BatteryUsageStatsProvider

This is being done in preparation for a switch of BatteryStats.dumpLocked
from BatteryStatsHelper to BatteryUsageStats

Bug: 162380414
Test: atest FrameworksCoreTests:com.android.internal.os.BatteryStatsTests

Change-Id: Ia8bf02116517c77f008b85c2012f68353b39c044
4 files changed