refactor: Split chat view into multiple files

lib/pages/chat/chat_emoji_picker.dart

@@ -0,0 +1,26 @@
+import 'package:flutter/material.dart';
+
+import 'package:emoji_picker_flutter/emoji_picker_flutter.dart';
+
+import 'chat.dart';
+
+class ChatEmojiPicker extends StatelessWidget {
+  final ChatController controller;
+  const ChatEmojiPicker(this.controller, {Key key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedContainer(
+      duration: const Duration(milliseconds: 300),
+      height: controller.showEmojiPicker
+          ? MediaQuery.of(context).size.height / 2
+          : 0,
+      child: controller.showEmojiPicker
+          ? EmojiPicker(
+              onEmojiSelected: controller.onEmojiSelected,
+              onBackspacePressed: controller.cancelEmojiPicker,
+            )
+          : null,
+    );
+  }
+}