Don't show "Clear All" w/ redacted notifs

The logic that determined when to show the Clear All Silent button in the
Silent notification header was occurring when the Silent (and Minimized)
sections update. At this time, there was no up-to-date information about
whether or not the notification has senstive content
(SensitiveContentCoordinator occurs later in the pipeline), and no
information about whether or not sensitive content can even be shown or
must be redacted (handled by NotificationStackScrollLayoutController).

Additionally, the visibility of the Clear All button in the shade footer
wasn't being adjusted at all under the new pipeline.

To remedy this, the following changes were made in this CL:

1. `boolean NotificationEntry#isSensitive()` has been dismantled. Rather
than relying on some separate code to properly set this value at some
point, instead the concept of "Sensitive Content" is derived directly
from the SBN + Ranking, and is kept separate from the state of the
user's settings, as well as the state of the lockscreen (whether we
would currently need to redact).

2. NotificationLockscreenUserMananger is the de-facto place for tracking
and querying redaction state. This includes checking if the user's
settings *would* require redaction (#needsRedactionInPublic), and
whether a user is actually public (#isLockscreenPublicMode).

3. In order to keep clients in sync, a new observable interface is
exposed on NotificationLockscreenUserManager that clients can use to be
notified when to requery #needsRedactionInPublic, due to user settings
changes. This replaces NotificationEntry#OnSensitivityChangedListener

4. SensitiveContentCoordinator has been removed entirely; the pipeline
no longer needs to invoke NotificationEntry#setSenstive, since it no
longer exists.

5. NotifStats has been updated to include additional information
extracted from the NotifCollection necessary to dynamically query for
redaction in the View layer, without needed to re-process the entire
list; specifically, we track a Set of users that currently have
sensitive notifications in the shade. This set is tested against the
user's settings (tracked separately from the pipeline in
NotifLockscreenUserManager).

Test: atest
Test: 1. Turn on notification redaction (no sensitive contents on lockscreen)
      2. Receive a silent sensitive notification
      3. Lock the device
      4. Double tap camera
      5. expand shade
      Observe: Clear all hidden in footer and in silent header

Fixes: 213443266
Fixes: 230581048
Change-Id: Ibc66576d28a48f7c82cad875ed2dcb57a7b23f10
Merged-In: Ibc66576d28a48f7c82cad875ed2dcb57a7b23f10