[Sb] Implement the unified battery inside of BatteryMeterView

BatteryMeterView is a very old class, with logs of tangled behavior. It
isn't feasible to build out a completely separate LinearLayout subclass
that can be swapped in place of the existing code in order to pull off a
true refactor, since there is other layout code that would break.

So, this CL attemps to split up the internals of the BatteryMeterView
into two distinct cases: newStatusBarIcons() and !newStatusBarIcons().
Where possible,the logic is completely forked into a legacy impl and a
modern one.

Test: BatteryMeterViewTest
Bug: 314812750
Flag: ACONFIG com.android.settingslib.flags.new_status_bar_icons DEVELOPMENT
Change-Id: I979096af1eb2b9725a87ccf008fb0f236281a10f