Multi file uploads (#4358)

* Allow MediaPickerScreen users to select the media selection mode (single or multiple)

* Fix cancellation

* Add support for multiple media URLs on the MediaUploadPreviewScreen.

* Support processing more URLs on the `MediaUploadingPreprocessor` and sending more on the `MediaUploadPreviewScreen`

* Add feature flag for `multipleAttachmentUploadEnabled`

* Add a label showing the current preview item index in the MediaUploadPreviewScreen

* Add support for dragging and dropping or pasting multiple items at the same time.

* Support sharing more than one file through the share extension.

* Limit the number of items that can be shared in one go to 5.

* Fix unit tests

* Fix incorrect fatal error when dealing with single selection media pickers.

* Document the `multipleAttachmentUploadEnabled` usage in the context of the MediaPicker.

* Use a task group for processing selected media in the photo library picker.

* Use a task group for processing multiple selected media in the MediaUploadingPreprocessor

* Switch the maximum number of items that can be shared to 10.

* Allow multiple items to be pasted at the same time.

ElementX/Sources/Screens/MediaUploadPreviewScreen/View/MediaUploadPreviewScreen.swift

@@ -5,6 +5,7 @@
 // Please see LICENSE files in the repository root for full details.
 //
 
+import Combine
 import Compound
 import GameController
 import QuickLook
@@ -16,6 +17,7 @@ struct MediaUploadPreviewScreen: View {
     @Bindable var context: MediaUploadPreviewScreenViewModel.Context
     
     @State private var captionWarningFrame: CGRect = .zero
+    @State private var currentIndex = 0
     @FocusState private var isComposerFocussed
     
     private var title: String { ProcessInfo.processInfo.isiOSAppOnMac ? context.viewState.title ?? "" : "" }
@@ -23,8 +25,15 @@ struct MediaUploadPreviewScreen: View {
     
     var body: some View {
         mainContent
-            .id(context.viewState.url)
+            .id(context.viewState.mediaURLs)
             .ignoresSafeArea(edges: [.horizontal])
+            .safeAreaInset(edge: .top) {
+                if context.viewState.mediaURLs.count > 1 {
+                    Text("\(currentIndex + 1) / \(context.viewState.mediaURLs.count)")
+                        .font(.compound.bodySM)
+                        .foregroundColor(.compound.textSecondary)
+                }
+            }
             .safeAreaInset(edge: .bottom, spacing: 0) {
                 composer
                     .padding(.horizontal, 12)
@@ -50,8 +59,9 @@ struct MediaUploadPreviewScreen: View {
                 .foregroundColor(.compound.textSecondary)
                 .frame(maxWidth: .infinity, maxHeight: .infinity)
         } else {
-            PreviewView(fileURL: context.viewState.url,
-                        title: context.viewState.title)
+            PreviewView(mediaURLs: context.viewState.mediaURLs,
+                        title: context.viewState.title,
+                        currentIndex: $currentIndex)
         }
     }
     
@@ -154,11 +164,12 @@ struct MediaUploadPreviewScreen: View {
 }
 
 private struct PreviewView: UIViewControllerRepresentable {
-    let fileURL: URL
+    let mediaURLs: [URL]
     let title: String?
+    @Binding var currentIndex: Int
 
     func makeUIViewController(context: Context) -> UIViewController {
-        let previewController = PreviewViewController()
+        let previewController = PreviewViewController(currentIndex: $currentIndex)
         previewController.dataSource = context.coordinator
         previewController.delegate = context.coordinator
         
@@ -185,11 +196,11 @@ private struct PreviewView: UIViewControllerRepresentable {
         // MARK: - QLPreviewControllerDataSource
         
         func numberOfPreviewItems(in controller: QLPreviewController) -> Int {
-            1
+            view.mediaURLs.count
         }
 
         func previewController(_ controller: QLPreviewController, previewItemAt index: Int) -> QLPreviewItem {
-            PreviewItem(previewItemURL: view.fileURL, previewItemTitle: view.title)
+            PreviewItem(previewItemURL: view.mediaURLs[index], previewItemTitle: view.title)
         }
         
         // MARK: - QLPreviewControllerDelegate
@@ -211,6 +222,28 @@ private class PreviewItem: NSObject, QLPreviewItem {
 }
 
 private class PreviewViewController: QLPreviewController {
+    private var cancellables: Set<AnyCancellable> = []
+    
+    init(currentIndex: Binding<Int>) {
+        super.init(nibName: nil, bundle: nil)
+        
+        // Observation of currentPreviewItem doesn't work, so use the index instead.
+        publisher(for: \.currentPreviewItemIndex)
+            .sink { index in
+                DispatchQueue.main.async {
+                    if index != Int.max { // Because reasons
+                        currentIndex.wrappedValue = index
+                    }
+                }
+            }
+            .store(in: &cancellables)
+    }
+
+    @available(*, unavailable)
+    required init?(coder: NSCoder) {
+        fatalError()
+    }
+    
     override func viewWillLayoutSubviews() {
         super.viewWillLayoutSubviews()
         
@@ -228,7 +261,7 @@ struct MediaUploadPreviewScreen_Previews: PreviewProvider, TestablePreview {
     static let snapshotURL = URL.picturesDirectory
     static let testURL = Bundle.main.url(forResource: "AppIcon60x60@2x", withExtension: "png")
     
-    static let viewModel = MediaUploadPreviewScreenViewModel(url: snapshotURL,
+    static let viewModel = MediaUploadPreviewScreenViewModel(mediaURLs: [snapshotURL],
                                                              title: "App Icon.png",
                                                              isRoomEncrypted: true,
                                                              shouldShowCaptionWarning: true,