Icon picker: Styling improvements

Instead of a the plain appearance of a EntityHeaderController, make the top icon bigger and use the same circled style as the choices in the list. Also highlight the current icon in the list as selected, even if it is the default for the mode type.

Also cleaned up controllers that don't need a ZenModesBackend to not receive it.

(Both of these changes also line up with the "new mode" fragment that is incoming).

Bug: 333901673
Bug: 326442408
Test: atest com.android.settings.notification.modes
Flag: android.app.modes_ui
Change-Id: I0c9f3e34019a1a6c48658933dde545ad8d7399ae