Set the light status bar flag if not in dark mode

To make the status bar content clearly visible we should set the light
status bar flag if the device is not in dark mode.

Bug: 241274551
Test: 1. Add an account and setup fingerprint unlock
      2. Go to "Settings>Passwords & accounts>add account" to add
         another account
      3. Wait for BiometricPrompt to pop up and check the status bar.
Change-Id: I7208b9c18c3734d150dfaaef6724948bd197066a