add settings for image packs

Closes #131

lib/helpers/extensions/build_event_options.dart

@@ -144,7 +144,7 @@ extension BuildEventOptions on Event {
                       (context) => EmojiPicker(
                         roomId: roomId,
                         allowFreeText: true,
-                        onSelection: (emoji, {shortcode}) {
+                        onSelection: (emoji, {shortcode, description}) {
                           Navigator.of(context).pop();
                           ref
                               .read(notifier)

lib/helpers/extensions/room_image_packs.dart

@@ -0,0 +1,34 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:nexus/models/content/content.dart";
+import "package:nexus/models/content/image_pack.dart";
+import "package:nexus/models/event.dart";
+import "package:nexus/models/image_pack.dart";
+import "package:nexus/models/room.dart";
+
+extension RoomImagePacks on Room {
+  /// The room's image packs by state key, preferring the stable type when a
+  /// pack has both, and leaving out deleted ones. [roomId] names those without
+  /// a name when the room has none either.
+  IMap<String, ImagePack> imagePacks(String roomId) => .fromEntries(
+    const [EventType.legacyImagePack, EventType.imagePack].expand(
+      (type) => (state[type.type] ?? .new()).entries
+          .map(
+            (entry) => switch (events[entry.value]) {
+              Event(redactedBy: null, content: final ImagePackContent content)
+                  when content.hasContent =>
+                MapEntry(
+                  entry.key,
+                  ImagePack.fromContent(
+                    content,
+                    roomId: roomId,
+                    roomName: metadata?.name ?? roomId,
+                    stateKey: entry.key,
+                  ),
+                ),
+              _ => null,
+            },
+          )
+          .nonNulls,
+    ),
+  );
+}