Extract snapshot persist thread from TaskSnapshotPersister(1/N)

Extract the IO thread and queue handler to SnapshotPersistQueue from
TaskSnapshotPersister, which will handle the snapshot IO tasks for both
Task and Activity snapshot.
The Persister and Loader class just need to create a different
PersistInfoProvider if something need to specify with different config.

Bug: 207481538
Test: atest TaskSnapshotPersisterLoaderTest TaskSnapshotCacheTest
TaskSnapshotLowResDisabledTest

Change-Id: Id739aca9eaeff7935ebf4b5f9a8ebc7bcd2779c7