Implement the hide silent notifications toggle

Implement the hide silent notifications toggle on the notifications
on lock screen page. This toggle will become invisible when the main
toggle is unset. This toogle will replace the existing Notifications
- notifications on the lock screen - hide silent conversations and
notifications preference when the flag is enabled.

Bug: 367455695
Flag: com.android.server.notification.notification_lock_screen_settings
Test: adb shell settings put secure \
 lock_screen_show_silent_notifications <1|0>
Change-Id: Icc0b26afd199ec3f14237fd1cdb27981383ae69f