Send/Receive support for reaction read syncs

ts/types/Reactions.ts

@@ -0,0 +1,11 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+export type ReactionType = Readonly<{
+  conversationId: string;
+  emoji: string;
+  fromId: string;
+  messageReceivedAt: number;
+  targetAuthorUuid: string;
+  targetTimestamp: number;
+}>;