BatteryMonitor: get battery health data from sys file nodes

Requirements for battery health aidl hal v2, include sysfs nodes:
  - Battery state of health
  - Charging state
  - Charging policy
  - Date of manufacturing of the battery
  - Date of first use of the battery

and functions
  - setChargingPolicy
  - getChargingPolicy
  - getBatteryHealthData

Bug: 251425963
Test: m
Change-Id: I210dc403ba95b1b75759227f84bc32f32be1bbaf
Signed-off-by: Jack Wu <wjack@google.com>