Copy smearing method to BatteryStatsHelper

This cl adds the following data in BatterySipper
1. screenPowerMah: power smeared by screen
2. proportionalSmearMah: power need to smeared proportionally
3. displayPowerMah: smeared power usage

This cl also copies bunch of methods from BatteryUtils to
BatteryStatsHelper with minor changes, so we could log smearing
logic in BatteryStatsHelper

Bug: 62300864
Test: runtest -x BatteryStatsHelperTest
Change-Id: I9f92f5c1ac5fa483d0c15a3d5daad570da68a7ff
Merged-In: I9f92f5c1ac5fa483d0c15a3d5daad570da68a7ff