Implement TIP3.

Use a target background battery drain rate to determine the consumption
limit (stock).

Bug: 249365572
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/tare
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/tare
Test: manually drain device and check calculation as it charges
Change-Id: I85879ed23365c388f2ff179c28973e8a2e72b827