Take into account creators when checking power levels (#44)

Fixes #40.

Reviewed-on: Nexus/nexus#44
Reviewed-by: Henry Hiles <henry@henryhiles.com>

lib/controllers/room_creators_controller.dart

@@ -0,0 +1,33 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/models/content/content.dart";
+import "package:nexus/models/content/create.dart";
+import "package:nexus/models/room.dart";
+
+class RoomCreatorsController extends Notifier<IList<String>> {
+  final Room room;
+  RoomCreatorsController(this.room);
+
+  @override
+  IList<String> build() {
+    final createRowId = room.state[EventType.create.type]?[""];
+    final createEvent = createRowId == null ? null : room.events[createRowId];
+
+    if (createEvent == null) return .new();
+
+    final createEventContent = switch (createEvent.content) {
+      CreateContent content => content,
+      _ => null,
+    };
+
+    return switch (createEventContent?.additionalCreatorIds) {
+      IList<String> creators => creators.add(createEvent.sender),
+      _ => .new([createEvent.sender]),
+    };
+  }
+
+  static final provider =
+      NotifierProvider.family<RoomCreatorsController, IList<String>, Room>(
+        RoomCreatorsController.new,
+      );
+}