Add check for disableSnapshot in TaskSnapshotPersister

This is to avoid queuing RemoveObsoleteFilesQueueItem and
DeleteWriteQueueItem, that would needlessly wake up the persister
thread.

Bug: 387915176
Flag: com.android.window.flags.check_disabled_snapshots_in_task_persister
Change-Id: I02f48ced909061dcc3ea55ee18800353c174b453