Display smart replies in notifications

If a notification contains a RemoteInput with non-empty choices,
NotificationContentView will add a SmartReplyView to
smart_reply_container in the expanded notification layout (if present).

This feature is guarded behind
Settings.Global.ENABLE_SMART_REPLIES_IN_NOTIFICATIONS.

Screenshot: https://screenshot.googleplex.com/jEzeL2ZYLMj.png

Bug: 67765414
Test: Viewed a notification with smart replies from Android Messages
Change-Id: I24d16df086edb58f51ae63830212d68166c74f52