fix live photo play button not updating

mobile/lib/providers/asset_viewer/is_motion_video_playing.provider.dart

@@ -0,0 +1,23 @@
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+
+/// Whether to display the video part of a motion photo
+final isPlayingMotionVideoProvider =
+    StateNotifierProvider<IsPlayingMotionVideo, bool>((ref) {
+  return IsPlayingMotionVideo(ref);
+});
+
+class IsPlayingMotionVideo extends StateNotifier<bool> {
+  IsPlayingMotionVideo(this.ref) : super(false);
+
+  final Ref ref;
+
+  bool get playing => state;
+
+  set playing(bool value) {
+    state = value;
+  }
+
+  void toggle() {
+    state = !state;
+  }
+}