Made a storage provider interface and both classic and avalonia impl.

Progrart.Core/Storage/IStorageProvider.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Progrart.Core.Storage
+{
+	public interface IStorageProvider
+	{
+		Task<Stream?> TryOpenRead(string path);
+		Task<Stream?> TryOpenWrite(string path);
+	}
+}