Final (?) touches to people/apps/sound circles

* Support comparing icon sets with a custom equivalence (needed because AppEntry doesn't implement equals(), and somewhat tricky because CircularIconPreference itself is not generic).
* Use final icons for allowed sounds.
* Use final appearance for +n icon.

Test: atest com.android.settings.notification.modes
Bug: 346551087
Flag: android.app.modes_ui
Change-Id: Iceadf4a182e607111afb72ff36bca872a62ae040