Prepare to move `CreateInferred`

Part of: #11907

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -419,6 +419,8 @@ namespace Microsoft.AspNetCore.Components
     }
     public static partial class RuntimeHelpers
     {
+        public static Microsoft.AspNetCore.Components.EventCallback<T> CreateInferredEventCallback<T>(object receiver, System.Action<T> callback, T value) { throw null; }
+        public static Microsoft.AspNetCore.Components.EventCallback<T> CreateInferredEventCallback<T>(object receiver, System.Func<T, System.Threading.Tasks.Task> callback, T value) { throw null; }
         public static T TypeCheck<T>(T value) { throw null; }
     }
     public partial class UIChangeEventArgs : Microsoft.AspNetCore.Components.UIEventArgs

src/Components/Components/src/RuntimeHelpers.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Threading.Tasks;
 
 namespace Microsoft.AspNetCore.Components
 {
@@ -17,6 +18,43 @@ namespace Microsoft.AspNetCore.Components
         /// <typeparam name="T"></typeparam>
         /// <param name="value"></param>
         /// <returns></returns>
+        //
+        // This method is used to create an expression binding site with a compile-time known type. This helps with providing
+        // good error messages, as well as proper method-group-to-delegate conversion when assigning component parameters.
         public static T TypeCheck<T>(T value) => value;
+
+        /// <summary>
+        /// Not intended for use by application code.
+        /// </summary>
+        /// <param name="receiver"></param>
+        /// <param name="callback"></param>
+        /// <param name="value"></param>
+        /// <returns></returns>
+        //
+        // This method is used with `@bind-Value` for components. When a component has a generic type, it's
+        // really messy to write to try and write the parameter type for ValueChanged - because it can contain generic
+        // type parameters. We're using a trick of type inference to generate the proper typing for the delegate
+        // so that method-group-to-delegate conversion works.
+        public static EventCallback<T> CreateInferredEventCallback<T>(object receiver, Action<T> callback, T value)
+        {
+            return EventCallback.Factory.Create<T>(receiver, callback);
+        }
+
+        /// <summary>
+        /// Not intended for use by application code.
+        /// </summary>
+        /// <param name="receiver"></param>
+        /// <param name="callback"></param>
+        /// <param name="value"></param>
+        /// <returns></returns>
+        //
+        // This method is used with `@bind-Value` for components. When a component has a generic type, it's
+        // really messy to write to try and write the parameter type for ValueChanged - because it can contain generic
+        // type parameters. We're using a trick of type inference to generate the proper typing for the delegate
+        // so that method-group-to-delegate conversion works.
+        public static EventCallback<T> CreateInferredEventCallback<T>(object receiver, Func<T, Task> callback, T value)
+        {
+            return EventCallback.Factory.Create<T>(receiver, callback);
+        }
     }
 }