refactor: Split chat view into multiple files

lib/pages/chat/tombstone_display.dart

@@ -0,0 +1,42 @@
+import 'package:flutter/material.dart';
+
+import 'package:flutter_gen/gen_l10n/l10n.dart';
+import 'package:matrix/matrix.dart';
+
+import 'chat.dart';
+
+class TombstoneDisplay extends StatelessWidget {
+  final ChatController controller;
+  const TombstoneDisplay(this.controller, {Key key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    if (controller.room.getState(EventTypes.RoomTombstone) == null) {
+      return Container();
+    }
+    return SizedBox(
+      height: 72,
+      child: Material(
+        color: Theme.of(context).secondaryHeaderColor,
+        elevation: 1,
+        child: ListTile(
+          leading: CircleAvatar(
+            foregroundColor: Theme.of(context).colorScheme.secondary,
+            backgroundColor: Theme.of(context).backgroundColor,
+            child: const Icon(Icons.upgrade_outlined),
+          ),
+          title: Text(
+            controller.room
+                .getState(EventTypes.RoomTombstone)
+                .parsedTombstoneContent
+                .body,
+            maxLines: 1,
+            overflow: TextOverflow.ellipsis,
+          ),
+          subtitle: Text(L10n.of(context).goToTheNewRoom),
+          onTap: controller.goToNewRoomAction,
+        ),
+      ),
+    );
+  }
+}