Implement the save action when previewing media. (#3630)

* Implement the save action on the media preview.

* Update Compound and use the correct icon.

Also fixes an icon that has been renamed.

* Update the add to photo library usage description to match the designs.

* PR comments.

ElementX/Sources/Screens/FilePreviewScreen/PhotoLibraryManager.swift

@@ -0,0 +1,37 @@
+//
+// Copyright 2024 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only
+// Please see LICENSE in the repository root for full details.
+//
+
+import Photos
+
+enum PhotoLibraryManagerError: Error {
+    case notAuthorized
+    case unknown(Error)
+}
+
+// sourcery: AutoMockable
+protocol PhotoLibraryManagerProtocol {
+    func addResource(_ type: PHAssetResourceType, at url: URL) async -> Result<Void, PhotoLibraryManagerError>
+}
+
+struct PhotoLibraryManager: PhotoLibraryManagerProtocol {
+    func addResource(_ type: PHAssetResourceType, at url: URL) async -> Result<Void, PhotoLibraryManagerError> {
+        do {
+            try await PHPhotoLibrary.shared().performChanges {
+                let request = PHAssetCreationRequest.forAsset()
+                let options = PHAssetResourceCreationOptions()
+                request.addResource(with: type, fileURL: url, options: options)
+            }
+            return .success(())
+        } catch {
+            if (error as NSError).code == PHPhotosError.accessUserDenied.rawValue {
+                return .failure(.notAuthorized)
+            } else {
+                return .failure(.unknown(error))
+            }
+        }
+    }
+}