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/Timeline/TimelineInteractionHandler.swift

@@ -14,7 +14,7 @@ enum TimelineInteractionHandlerAction {
     case displayEmojiPicker(itemID: TimelineItemIdentifier, selectedEmojis: Set<String>)
     case displayReportContent(itemID: TimelineItemIdentifier, senderID: String)
     case displayMessageForwarding(itemID: TimelineItemIdentifier)
-    case displayMediaUploadPreviewScreen(url: URL)
+    case displayMediaUploadPreviewScreen(mediaURLs: [URL])
     case displayPollForm(mode: PollFormMode)
     
     case showActionMenu(TimelineItemActionMenuInfo)
@@ -277,7 +277,7 @@ class TimelineInteractionHandler {
     
     // MARK: Pasting and dropping
     
-    func handlePasteOrDrop(_ provider: NSItemProvider) {
+    func handlePasteOrDrop(_ providers: [NSItemProvider]) {
         Task {
             let loadingIndicatorIdentifier = UUID().uuidString
             self.userIndicatorController.submitIndicator(UserIndicator(id: loadingIndicatorIdentifier, type: .modal, title: L10n.commonLoading, persistent: true))
@@ -285,13 +285,19 @@ class TimelineInteractionHandler {
                 self.userIndicatorController.retractIndicatorWithId(loadingIndicatorIdentifier)
             }
             
-            guard let fileURL = await provider.storeData() else {
-                MXLog.error("Failed storing NSItemProvider data \(provider)")
-                self.actionsSubject.send(.displayErrorToast(L10n.screenRoomErrorFailedProcessingMedia))
-                return
+            var mediaURLs = [URL]()
+            for provider in providers {
+                if let fileURL = await provider.storeData() {
+                    mediaURLs.append(fileURL)
+                } else {
+                    MXLog.error("Failed storing NSItemProvider data \(provider)")
+                    self.actionsSubject.send(.displayErrorToast(L10n.screenRoomErrorFailedProcessingMedia))
+                }
             }
             
-            self.actionsSubject.send(.displayMediaUploadPreviewScreen(url: fileURL))
+            if !mediaURLs.isEmpty {
+                self.actionsSubject.send(.displayMediaUploadPreviewScreen(mediaURLs: mediaURLs))
+            }
         }
     }