porting shell from nuget to local

src/Shared/Microsoft.Windows.Shell/Standard/BLENDFUNCTION.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Standard
+{
+	internal struct BLENDFUNCTION
+	{
+		public AC BlendOp;
+
+		public byte BlendFlags;
+
+		public byte SourceConstantAlpha;
+
+		public AC AlphaFormat;
+	}
+}