Merge NotificationsSoundPolicyRepository and ZenModeRepository

These were essentially doing the same thing in slightly different ways.
NotificationsSoundPolicyRepository is the one we're keeping under a new
name: it uses BroadcastReceiver to listen for policy changes.
Meanwhile, the other ZenModeRepository was using ZenModeController, which
in turn uses ContentObserver to listen for changes. In the long run, we
want to replace the callback-based ZenModeController with flows, so this
is one step towards that goal.

Note that the notificationPolicy flow in the old
NotificationSoundPolicyRepository was actually returning the
consolidatedNotificationPolicy. To make it more explicit, I included
both in the new repository, but changed the existing users of
notificationPolicy to use consolidatedNotificationPolicy to avoid a
behavior change.

Also replaced the ZenMode class with a simple int to avoid confusion
with the ZenMode class we're introducing from settings in a follow-up
CL. The only thing it was doing was validation, but that's not strictly
necessary since every consumer of this value (aka the interactors) has
to decide what to do with an "unknown" value anyway.

Bug: 308591859
Bug: 346519570
Test: ZenModeRepositoryTest
Flag: android.app.modes_api
Flag: com.android.systemui.new_volume_panel
Flag: com.android.systemui.notifications_footer_view_refactor
Change-Id: Ie02480dec05055ad3d7c24bd16c76f91bc64c58c