Implement the show sensitive content only when unlocked toggle on the
notifications on lock screen page. The toggle will become invisible
when the main toggle is unset or when there's no screen locks.
Bug: 367455695
Flag: com.android.server.notification.notification_lock_screen_settings
Test: adb shell settings get secure \
lock_screen_allow_private_notifications <1|0>
Change-Id: I174478540c4cc2e2df7047049671266041dd41cf
c16c9b2df6