Add PowerStatsAggregator to aggregate power stats

This aggregator iterates over battery history and
aggregates power stats on  a per battery state,
per screen state, per UID, per proc state basis.

Bug: 292296001
Test: atest FrameworksServicesTests:BatteryStatsTests
Test: adb shell dumpsys batterystats --aggregated
Change-Id: I1d2ca51254c1e46eedb4e8bb88673e0c65501769