Add battery discharge prediction APIs.

This CL adds an API to enable an external app to provide the system with
an estimate of how much time is remaining until the battery reaches 0%.
This information will be used in Settings and SysUI to display the
estimated time until the device is fully discharged.

Bug: 139413884
Test: atest android.os.cts.PowerManagerTest
Test: atest android.permission.cts.PowerManagerServicePermissionTest
Test: atest CtsPermission2TestCases
Test: atest SettingsProviderTest
Change-Id: I7073c521e392e9616111e5e80b92a11285ac6c91