Add get_incremental_snapshot_hash_for_node() to gossip

Fixes #20377

gossip/src/cluster_info.rs

@@ -1115,6 +1115,18 @@ impl ClusterInfo {
         Some(map(hashes))
     }
 
+    pub fn get_incremental_snapshot_hash_for_node<F, Y>(&self, pubkey: &Pubkey, map: F) -> Option<Y>
+    where
+        F: FnOnce((Slot, &Vec<(Slot, Hash)>)) -> Y,
+    {
+        let gossip_crds = self.gossip.crds.read().unwrap();
+        let incremental_snapshot_hash = &gossip_crds.get::<&IncrementalSnapshotHash>(*pubkey)?;
+        Some(map((
+            incremental_snapshot_hash.base_slot,
+            incremental_snapshot_hash.hashes,
+        )))
+    }
+
     /// Returns epoch-slots inserted since the given cursor.
     /// Excludes entries from nodes with unkown or different shred version.
     pub fn get_epoch_slots(&self, cursor: &mut Cursor) -> Vec<EpochSlots> {