Add a fullscreen button to TimelineMediaPreviewScreen and hook up swiping through the timeline. (#3638)

* Add a fullscreen button to media previews - Not ideal but the gestures conflict with the preview controller.

* Don't un-flip the preview thumbnail until the preview has disappeared, and only do it on iOS 18.

* Add all of the loaded items for previewing in the preview controller.

ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewModels.swift

@@ -15,11 +15,19 @@ enum TimelineMediaPreviewViewModelAction: Equatable {
 }
 
 struct TimelineMediaPreviewViewState: BindableState {
+    /// All of the items in the timeline that can be previewed.
     var previewItems: [TimelineMediaPreviewItem]
+    /// The index of the initial item inside of `previewItems` that is to be shown.
+    let initialItemIndex: Int
+    
+    /// The media item that is currently being previewed.
     var currentItem: TimelineMediaPreviewItem
+    /// All of the available actions for the current item.
     var currentItemActions: TimelineItemMenuActions?
     
+    /// The namespace used for the zoom transition.
     let transitionNamespace: Namespace.ID
+    /// A publisher that the view model uses to signal to the QLPreviewController when the current item has been loaded.
     let fileLoadedPublisher = PassthroughSubject<TimelineItemIdentifier, Never>()
     
     var bindings = TimelineMediaPreviewViewStateBindings()
@@ -49,6 +57,21 @@ class TimelineMediaPreviewItem: NSObject, QLPreviewItem, Identifiable {
         self.timelineItem = timelineItem
     }
     
+    init?(roomTimelineItemViewState: RoomTimelineItemViewState) {
+        switch roomTimelineItemViewState.type {
+        case .audio(let audioRoomTimelineItem):
+            timelineItem = audioRoomTimelineItem
+        case .file(let fileRoomTimelineItem):
+            timelineItem = fileRoomTimelineItem
+        case .image(let imageRoomTimelineItem):
+            timelineItem = imageRoomTimelineItem
+        case .video(let videoRoomTimelineItem):
+            timelineItem = videoRoomTimelineItem
+        default:
+            return nil
+        }
+    }
+    
     // MARK: Identifiable
     
     var id: TimelineItemIdentifier { timelineItem.id }