BatteryService: Use android.hardware.health@2.0.

- BatteryService talks to android.hardware.health@2.0::IHealth
  /default and /backup instances.
- /default is optionally implemented by vendor (for launch devices)
  and overrides /backup if it exist.
- /backup is served by healthd (for upgrading devices) and
  is the fallback option.

Before this change, BatteryService talks to healthd in binder.
This change switches to hwbinder for this communication. The information
flow between them stays the same (and is augmented with a follow-up
CL for BatteryManager).

Test: adb logcat -e "health@2.0"
Test: vts health test
Test: BatteryManagerTest

Bug: 62229583
Change-Id: I46c4c0746a579b76c94660d062b92b9a9c4a4dbd