Added single row value delegate interfaces

src/ImageSharp/Advanced/IRowAction.cs

@@ -0,0 +1,17 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Advanced
+{
+    /// <summary>
+    /// Defines the contract for an action that operates on a row.
+    /// </summary>
+    public interface IRowAction
+    {
+        /// <summary>
+        /// Invokes the method passing the row y coordinate.
+        /// </summary>
+        /// <param name="y">The row y coordinate.</param>
+        void Invoke(int y);
+    }
+}

src/ImageSharp/Advanced/IRowAction{TBuffer}.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+
+namespace SixLabors.ImageSharp.Advanced
+{
+    /// <summary>
+    /// Defines the contract for an action that operates on a row with a temporary buffer.
+    /// </summary>
+    /// <typeparam name="TBuffer">The type of buffer elements.</typeparam>
+    public interface IRowAction<TBuffer>
+        where TBuffer : unmanaged
+    {
+        /// <summary>
+        /// Invokes the method passing the row and a buffer.
+        /// </summary>
+        /// <param name="y">The row y coordinate.</param>
+        /// <param name="span">The contiguous region of memory.</param>
+        void Invoke(int y, Span<TBuffer> span);
+    }
+}