Fix the misleading issue for battery saver notification

- Replace the full battery icon with battery saver icon on turning on
battery saver notification.
- Replace the full battery icon with settings gear icon on turning off
battery saver notification.

Bug: 360725512
Test: Unit Test
Flag: EXEMPT for bug fix
Change-Id: I085fbbf30845ed1e5a61e043c4abb91bcee2ba54