fix: FileStorage.CopyAsync should open target stream for write

src/Uno.UI.RuntimeTests/Tests/Windows_Storage/Given_StorageFile.cs

@@ -383,6 +383,21 @@ public async Task When_GetFileFromApplicationUriAsync_Is_Passed_AppData()
 			Assert.IsTrue(bytes1.SequenceEqual(bytes2));
 		}
 
+#if __ANDROID__
+		[TestMethod]
+		public async Task When_Copy_Saf()
+		{
+			var file1 = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///Assets/ingredient3.png"));
+			await file1.CopyAsync(ApplicationData.Current.LocalCacheFolder, "ingredient3.png", NameCollisionOption.ReplaceExisting);
+
+			var directory = new Java.IO.File(ApplicationData.Current.LocalCacheFolder.Path);
+			var documentFile = AndroidX.DocumentFile.Provider.DocumentFile.FromFile(directory).CreateFile("image/png", "ingredient3.png");
+
+			var file2 = StorageFile.GetFromSafDocument(documentFile);
+			await file2.CopyAsync(ApplicationData.Current.LocalFolder, "When_Copy_Saf_uno_logo.png", NameCollisionOption.ReplaceExisting);
+		}
+#endif
+
 		private string GetRandomFilePath()
 			=> Path.Combine(ApplicationData.Current.LocalFolder.Path, $"{Guid.NewGuid()}.txt");
 

src/Uno.UWP/Storage/StorageFile.Base.cs

@@ -75,7 +75,7 @@ public virtual async Task<StorageFile> CopyAsync(CancellationToken ct, IStorageF
 			public virtual async Task CopyAndReplaceAsync(CancellationToken ct, IStorageFile target)
 			{
 				using (var src = await Owner.OpenStreamForReadAsync())
-				using (var dst = await target.OpenStreamForReadAsync())
+				using (var dst = await target.OpenStreamForWriteAsync())
 				{
 					await src.CopyToAsync(dst, Buffer.DefaultCapacity, ct);
 				}