Adding some interfaces for event conversions.

AsyncRx.NET/System.Reactive.Shared/System/Reactive/IEventPatternSource.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+namespace System.Reactive
+{
+    /// <summary>
+    /// Represents a data stream signaling its elements by means of an event.
+    /// </summary>
+    /// <typeparam name="TEventArgs">The type of the event data generated by the event.</typeparam>
+    public interface IEventPatternSource<TEventArgs>
+    {
+        /// <summary>
+        /// Event signaling the next element in the data stream.
+        /// </summary>
+        event EventHandler<TEventArgs> OnNext;
+    }
+}

AsyncRx.NET/System.Reactive.Shared/System/Reactive/IEventSource.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+namespace System.Reactive
+{
+    /// <summary>
+    /// Represents a data stream signaling its elements by means of an event.
+    /// </summary>
+    /// <typeparam name="T">
+    /// The type of the event data generated by the event.
+    /// This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
+    /// </typeparam>
+    public interface IEventSource<out T>
+    {
+        /// <summary>
+        /// Event signaling the next element in the data stream.
+        /// </summary>
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1710:IdentifiersShouldHaveCorrectSuffix", Justification = "By design.")]
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1009:DeclareEventHandlersCorrectly", Justification = "Can't do this for Action<T>.")]
+        event Action<T> OnNext;
+    }
+}