[SB] Fix performance regression in UnifiedBattery

In ag/34554445 we moved all the state reads
out of the draw phase. This caused a performance
regression.

Test: Manual
Test: BatteryScreenshotTest
Bug: 432263294
Flag: com.android.settingslib.flags.new_status_bar_icons
Change-Id: Ie88625f14507fe96a490ad9f2f42b506f99216a2