* Add `CacheBitmapLoader`.
* Add `CacheBitmapLoaderTest`.
* Remove the `BitmapLoadRequest` and some bitmap caching logic in `DefaultMediaNotificationProvider` since we moved all of them in `CacheBitmapLoader`.
* Modify `DefaultMediaNotificationProviderTest`.
PiperOrigin-RevId: 482787445
(cherry picked from commit ca4edff1)
