Implement the V2 notification minimalism prototype

* Only notifications in the Media, Heads Up, or FGS buckets can show outside the shelf on the lock screen.
* The top unseen notification is sectioned no lower than the FGS notifications.
* The top unseen notification is (by default) promoted out of its group so that it can be shown on lockscreen.
* Unseen notifications are still tracked the same as with the tangor behavior, but can be seen in the locked shade.

Bug: 330387368
Test: manual
Flag: com.android.systemui.notification_minimalism_prototype
Change-Id: Ic390064d713d5355ce56005b7a61f5d0ee9fd698