Don't show the security screen on devicePolicyManager changes

Instead, we just want to update the current security mode
and pause the previous security mode.

We do this to avoid unnecessarily focusing on the
InputView on the lockscreen to avoid key events
from being directed to an invisible view.

Bug: 417307529
Test: Enable debug logs; when changing
  the pin/pattern/password, observe no
  showSecurityScreen log
Test: manual
  From lock screen:
    - adb shell locksettings set-pin "1234"
    - swipe up to show bouncer, then click back
    - adb shell locksettings clear --old "1234"
    - adb shell wm dismiss-keyguard
    Observe: keyguard dismisses; bouncer doesn't show
Flag: com.android.systemui.bouncer_lifecycle_fix
Change-Id: I4388975fe231e23d8263ccddd5d5c2c4e881e110