Move bunch of battery methods to BatteryUtils.java

This cl moves following methods to BatteryUtils:
1. shouldHideSipper
2. removeHiddenBatterySippers
3. calculateBatteryPercent

As a result, we could use these methods in battery page as well
as app info page.

This cl also move bunch of tests to new file and add test for
method calculateBatteryPercent

Bug: 36816681
Test: RunSettingsRoboTests
Change-Id: Ic32700fe9741fbb96363db4af2d4fccb3ee8e317