Add Battery Health stats to pixelstats

The intent is to collect battery health data for improving battery life.
This reads from the health_index_stats node and reports different
battery health metrics based on different algorithms.

eldar/142490839

Bug: 230501230
Test: Ensure that the stats are reported correctly via pixelstats
Merged-In: I741212d427dc2304e6c4ac9eae4c20c4883bd06c
Change-Id: I0ab58ea7124f0c0727a0be377d688426f88b04f6
6 files changed