Replace MessageController with MessageCache

ts/util/getMessageConversation.ts

@@ -0,0 +1,13 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { MessageAttributesType } from '../model-types.d';
+import type { ConversationModel } from '../models/conversations';
+
+export function getMessageConversation({
+  conversationId,
+}: Pick<MessageAttributesType, 'conversationId'>):
+  | ConversationModel
+  | undefined {
+  return window.ConversationController.get(conversationId);
+}