Update status bar battery icon

 - Update low battery threshold to 20 since low battery warning
   already set as 20
 - Update battery saver render format and color
 screenshots:
   https://screenshot.googleplex.com/6MUsuq7McxAEpZg.png
   https://screenshot.googleplex.com/38RfSn8LwiZcJD5.png
   https://screenshot.googleplex.com/3bUVN4TCaeDdrDy.png
   https://screenshot.googleplex.com/3hJ9aNJwbLUiGSP.png
   https://screenshot.googleplex.com/S6xakjvHQu2aNMS.png

Bug: 265364329
Fix: 265364329
Test: make RunSettingsLibRoboTests
Change-Id: I72bd3f52db141835123dca83662354d462fb74a2