StateService: allow to enable StateService plugin from arbitraty height

Do not require StateService plugin to be enabled from genesis block.
Node can build MPT based on the current contract storage state from
scratch at the arbitrary height.

This feature is required to avoid chain resync from genesis for those
nodes who don't have StateService plugin enabled.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

Author: AnnaShaleva

src/Plugins/StateService/StatePlugin.cs

@@ -102,6 +102,25 @@ void ICommittingHandler.Blockchain_Committing_Handler(NeoSystem system, Block bl
             IReadOnlyList<ApplicationExecuted> applicationExecutedList)
         {
             if (system.Settings.Network != StateServiceSettings.Default.Network) return;
+
+            // Rebuild MPT from scratch on node bootstrap if StateService plugin is not up-to-date wrt the current block height.
+            if (block.Index > 0)
+            {
+                using var stateSnapshot = StateStore.Singleton.GetSnapshot();
+                var persistedHeight = block.Index - 1;
+                var stateRoot = stateSnapshot.GetStateRoot(persistedHeight);
+                if (stateRoot is null)
+                {
+                    using var coreSnapshot = system.GetSnapshotCache();
+                    StateStore.Singleton.UpdateLocalStateRootSnapshot(persistedHeight,
+                        coreSnapshot.Find(SeekDirection.Forward)
+                        .Where(si => si.Key.Id != NativeContract.Ledger.Id)
+                        .Select(si => new KeyValuePair<StorageKey, DataCache.Trackable>(si.Key, new DataCache.Trackable(si.Value, TrackState.Added)))
+                        .ToList());
+                    StateStore.Singleton.UpdateLocalStateRoot(persistedHeight);
+                }
+            }
+
             var root = StateStore.Singleton.UpdateLocalStateRootSnapshot(block.Index,
                 snapshot.GetChangeSet()
                     .Where(p => p.Value.State != TrackState.None && p.Key.Id != NativeContract.Ledger.Id)