feat: Implement room tombstones

lib/src/room.dart

@@ -18,6 +18,7 @@
 
 import 'dart:async';
 
+import 'package:famedlysdk/src/utils/tombstone_content.dart';
 import 'package:html_unescape/html_unescape.dart';
 import 'package:matrix_file_e2ee/matrix_file_e2ee.dart';
 
@@ -1665,4 +1666,14 @@ class Room {
       await client.handleSync(syncUpdate, sortAtTheEnd: sortAtTheEnd);
     }
   }
+
+  /// Whether this is an extinct room which has been archived in favor of a new
+  /// room which replaces this. Use [getLegacyRoomInformations] to get more
+  /// informations about it if this is true.
+  bool get isExtinct => getState(EventTypes.RoomTombstone) != null;
+
+  /// Returns informations about how this room is
+  TombstoneContent get extinctInformations => isExtinct
+      ? TombstoneContent.fromJson(getState(EventTypes.RoomTombstone).content)
+      : null;
 }

lib/src/utils/tombstone_content.dart

@@ -0,0 +1,15 @@
+class TombstoneContent {
+  String body;
+  String replacementRoom;
+
+  TombstoneContent.fromJson(Map<String, dynamic> json)
+      : body = json['body'],
+        replacementRoom = json['replacement_room'];
+
+  Map<String, dynamic> toJson() {
+    final data = <String, dynamic>{};
+    data['body'] = body;
+    data['replacement_room'] = replacementRoom;
+    return data;
+  }
+}