Show app icons in bundle header

New class AppData.kt holds info for fetching app icons
BundleRepository: replace previewIcons with AppData list
BundleInteractor: fetch Drawables for AppData via AppIconProvider
BundleHeader: get Drawables from BundleInteractor

Fixes: 415055105
Test: BundleCoordinatorTest
Test: screenrecord in bug
  adb shell setprop persist.debug.notification_bundle_ui_debug_app_name com.google.cinek.notify && adb reboot
  collapse bundle: icons appear
  expand bundle: icons hide
Flag: com.android.systemui.notification_bundle_ui
Change-Id: Id7a87c36d41d97e9afed4160e1e4a5efc8fc6bce