chore: move controllers from ui to core

Signed-off-by: xsahil03x <[email protected]>

packages/stream_chat_flutter/test/src/message_input/message_input_controller_test.dart

@@ -1,14 +0,0 @@
-import 'package:flutter_test/flutter_test.dart';
-import 'package:stream_chat_flutter/stream_chat_flutter.dart';
-
-void main() {
-  testWidgets(
-    'should instantiate a new MessageInputController with empty message',
-    (tester) async {
-      final controller = MessageInputController()..text = 'test';
-
-      expect(controller.text, 'test');
-      expect(controller.message.text, 'test');
-    },
-  );
-}