Add Battery slice in Contextual Settings Homepage

- Add Battery card that implements CustomSliceable in Contextual
Settings Homepage.
- Add test case for Battery slice.
- Created a loadBatteryInfo method for BatterySlice.
- Add a map in CustomSliceManager to cache CustomSliceable instances,
let existing battery slice be able to update battery info.
- Use a flag to avoid triggering an infinite loop when calling
notifyChange in the callback function.

Bug: 114796623, 115971399
Test: manual, robotests
Change-Id: I4b785708bf8456c6c4de7cae4b44f8a060bccbae