Add debug logging to SnapshotPersistQueue.

The crash only occur in Monkey test, add log to check what happen
and revert then. It is safe because those log are behind flag.

Bug: 424273966
Flag: com.android.window.flags.extending_persistence_snapshot_queue_depth
Test: Manual

Change-Id: I506599bb3dfc5c88c382357deabd963b1054c4d2