Refine battery settings layout

 - Add loading text to progress bar to prevent UI flaky
 - Setup enable/disable state for battery saver switch
 - Remove battery saver page divider

Bug: 177964551
Bug: 177964753
Bug: 184626649
Test: make SettingsRoboTests, visually
Change-Id: I8e05c0c0f02710729e1f59eff23fb3f425770de9
5 files changed