[42/n] Integrate LetterboxCleanupAdapter

The LetterboxCleanupAdapter allows to remove all the letterbox surfaces
for a Task that is removed. Just using TransactionObserver was not
completely reliable on some cases (e.g. close from Recents).

Flag: com.android.window.flags.app_compat_refactoring
Fix: 416222124
Test: m

Change-Id: Ied6d4ebd1274a47232e22f68db2eac35e427bbae