SnapshotPackagerService pushes incremental snapshot hashes to CRDS (#20442)

Now that CRDS supports incremental snapshot hashes,
SnapshotPackagerService needs to push 'em!

This commit does two main things:

1. SnapshotPackagerService now knows about incremental snapshot hashes,
   and will push SnapshotPackage::IncrementalSnapshot hashes to CRDS.
2. At startup, when loading from a full + incremental snapshot, the
   hashes need to be passed all the way to SnapshotPackagerService so it
   can push these starting hashes to CRDS.  Those values have been piped
   through.

Fixes #20441 and #20423

runtime/src/lib.rs

@@ -42,6 +42,7 @@ pub mod serde_snapshot;
 mod shared_buffer_reader;
 pub mod snapshot_archive_info;
 pub mod snapshot_config;
+pub mod snapshot_hash;
 pub mod snapshot_package;
 pub mod snapshot_utils;
 pub mod sorted_storages;