Notif redesign: Don't apply effects to app icons

In order to know if we're showing the app icon from places where we
can't inject NotificationIconStyleProvider, I added a property to
ExpandableNotificationRow. It's not ideal that now the
shouldShowAppIcon getter has side effects, but it's better than
attempting an overly complex solution to be able to access
NotificationRowIconView otherwise.

Bug: 371174789
Test: tested manually that e.g. icons in grouped messaging notifications
from Notify aren't greyed out
Flag: android.app.notifications_redesign_app_icons

Change-Id: I632daa937f237aa7bea22b9e7fd84939be1a5a34