Fixes to CircularIconsPreference & friends

Fixed view reuse. The views obtained from the ViewHolder should not be stored in Preference fields, since they can be rebound and thus a Preference can end up updating the wrong view.

Also added equivalence to the item class in the People segment so there is no flicker when the mode is reloaded.

Fixes: 346551087
Test: atest com.android.settings.notification.modes
Flag: android.app.modes_ui
Change-Id: Ibd89a826b19acabd9a46bb3ba2916453689636ed