feat(core, ui): add grid views, minor refactoring

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

packages/stream_chat_flutter/example/lib/tutorial_part_4.dart

@@ -145,7 +145,7 @@ class ThreadPage extends StatelessWidget {
             ),
           ),
           StreamMessageInput(
-            messageInputController: MessageInputController(
+            messageInputController: StreamMessageInputController(
               message: Message(parentId: parent!.id),
             ),
           ),

packages/stream_chat_flutter/example/lib/tutorial_part_6.dart

@@ -184,7 +184,7 @@ class ThreadPage extends StatelessWidget {
             ),
           ),
           StreamMessageInput(
-            messageInputController: MessageInputController(
+            messageInputController: StreamMessageInputController(
               message: Message(parentId: parent!.id),
             ),
           ),