Show an 'Undo' snackbar when users dismiss a predicted hotseat item.

Bug: 200841778
Test: Hard-coded the flag to be true, and verified that the snack bar
is shown with the correct text. Also verified that talkback announces
"Item Removed" properly and that the correct log event is produced by
the AppEventProducer which AiAi needs to process the user action.

Change-Id: Ifbb9cf7aecf26cd4bcebf48d4fb07fb3d5af46bb