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/RoomScreen/ComposerToolbar/View/ComposerToolbar.swift

@@ -181,8 +181,8 @@ struct ComposerToolbar: View {
             sendMessage()
         } editAction: {
             context.send(viewAction: .editLastMessage)
-        } pasteAction: { provider in
-            context.send(viewAction: .handlePasteOrDrop(provider: provider))
+        } pasteAction: { providers in
+            context.send(viewAction: .handlePasteOrDrop(providers: providers))
         } cancellationAction: {
             switch context.viewState.composerMode {
             case .edit:
@@ -259,7 +259,7 @@ struct ComposerToolbar: View {
                             viewModel: context.viewState.wysiwygViewModel,
                             itemProviderHelper: ItemProviderHelper(),
                             keyCommands: context.viewState.keyCommands) { provider in
-            context.send(viewAction: .handlePasteOrDrop(provider: provider))
+            context.send(viewAction: .handlePasteOrDrop(providers: [provider]))
         }
     }