[Thread Detail] [Part 1] TF-3639 data layer and controller (#3645)

lib/features/thread_detail/domain/repository/thread_detail_repository.dart

@@ -0,0 +1,9 @@
+import 'package:jmap_dart_client/jmap/account_id.dart';
+import 'package:jmap_dart_client/jmap/mail/email/email.dart';
+
+abstract class ThreadDetailRepository {
+  Future<List<EmailId>> getThreadById(
+    ThreadId threadId,
+    AccountId accountId,
+  );
+}