Add width and height to attachments in ActivityPub (mastodon#16245)

Co-authored-by: dogelover911 <dogelover911@localhost>

Author: dogelover911

app/serializers/activitypub/note_serializer.rb

@@ -170,6 +170,8 @@ class MediaAttachmentSerializer < ActivityPub::Serializer
 
     attributes :type, :media_type, :url, :name, :blurhash
     attribute :focal_point, if: :focal_point?
+    attribute :width, if: :width?
+    attribute :height, if: :height?
 
     has_one :icon, serializer: ActivityPub::ImageSerializer, if: :thumbnail?
 
@@ -204,6 +206,22 @@ def icon
     def thumbnail?
       object.thumbnail.present?
     end
+
+    def width?
+      object.file.meta&.dig('original', 'width').present?
+    end
+
+    def height?
+      object.file.meta&.dig('original', 'height').present?
+    end
+
+    def width
+      object.file.meta.dig('original', 'width')
+    end
+
+    def height
+      object.file.meta.dig('original', 'height')
+    end
   end
 
   class MentionSerializer < ActivityPub::Serializer