Rename Battery to BatteryState.

Rename Battery to BatteryState, and rename the method hasBattery to
isPresent.
Return NaN in getCapacity() if capacity can not be read.

Bug: 180733860
Test: atest android.hardware.input.cts.tests

Change-Id: I8e855be0b263479c2744b817df5f591c9d1e4a64