chore(firestore): add support for onSnapshotsInSync

packages/firestore/lib/modular/snapshot.d.ts

@@ -227,3 +227,13 @@
   left: Query<AppModelType, DbModelType>,
   right: Query<AppModelType, DbModelType>,
 ): boolean;
+
+/**
+ * Attaches a listener for a snapshots-in-sync event.
+ * The snapshots-in-sync event indicates that all listeners affected by a given change have fired, even if
+ * a single server-generated change affects multiple listeners.
+ *
+ * @param firestore
+ * @param onSync
+ */
+export declare function onSnapshotsInSync(firestore: Firestore, onSync: () => void): Unsubscribe;

packages/firestore/lib/modular/snapshot.js

@@ -18,3 +18,8 @@
 export function snapshotEqual(left, right) {
   return left.isEqual.call(left, right, MODULAR_DEPRECATION_ARG);
 }
+
+
+export function onSnapshotsInSync(firestore, ...args) {
+  return firestore.onSnapshotsInSync.call(firestore, ...args, MODULAR_DEPRECATION_ARG);
+}