Destroy activity in onStop()

Pixel Imprint will call onDestroy() whenever its menu is invisible.
(https://source.corp.google.com/tm-dev/packages/apps/Settings/src/com/android/settings/biometrics/fingerprint/FingerprintSettings.java;l=547?sq=package:tm-dev)
However, Screen lock should have the same behavior as Pixel Imprint but
it doesn't.
onDestroy() for Screen lock should be called whenever we exit the menu
or the menu becomes invisible. Otherwise, the password may be leaked to
RAM unexpectedly in some situations.

Bug: 233373529
Test: manual
Change-Id: Idc0c115fc2061d863f9cab2aed99c04340b827f8