[BatterySaver] Fix the vulnerability of ExtremeBatterySaver

Enable the Standard Battery Saver directly if this is the first time
that user see the low battery notification for enabling battery saver and
the device is locked.

Flag: com.android.settingslib.flags.extreme_power_low_state_vulnerability
Bug: 346513692
Test: Manual Test and Unit Test
Test: http://ab/I38500010293424439 (robotest)
Change-Id: Ie2538980f2b8fef46b213f39cb9f56bf17305e8c