Notification minimalism prototype update

* Now promotes both the top colorized ongoing notification and the top unseen notification. This means the max number of notifications can be 2.
* This is done by adding a second new sectioner used by this prototype for selecting the top ongoing notification.
* This also defines 2 new buckets, since top ongoing and top unseen are now new buckets separate from existing ones.
* This also excludes silent notifications from ever being promoted.

Bug: 330387368
Test: atest SystemUITests
Flag: com.android.systemui.notification_minimalism_prototype
Change-Id: I824db2a924f2cb528ecf18b1a417ef88e7a0d2be