Dump values in NotifCollectionCache, not just keys

This can be helpful for NotificationIconStyleProvider, where the values
are booleans. Not so much so for the AppIconProvider where we're just
printing the references to some drawables, but that's still okay, it's
not that much noise.

Bug: 371174789
Test: adb shell dumpsys activity service com.android.systemui/.SystemUIService AppIconProviderImpl NotificationIconStyleProviderImpl
Flag: android.app.notifications_redesign_app_icons
Change-Id: Ib22c1f09dbf877fd0e759b254e80a4747d9a5696