Create or rename a scramble folder for task snapshots.

Enhance file security by making the file path unpredictable and
difficult to guess.
Create or rename the scramble folder when first access happen.

Flag: com.android.window.flags.scramble_snapshot_file_name
Bug: 293139053
Test: atest TaskSnapshotCacheTest TaskSnapshotLowResDisabledTest
TaskSnapshotPersisterLoaderTest ActivitySnapshotControllerTests

Change-Id: Ie83e381f3a9fe32bdea6378103fd762251a5faa0