Add docs for AsyncInterfaces (#88432)

Author: ericstj

src/libraries/Microsoft.Bcl.AsyncInterfaces/src/Microsoft.Bcl.AsyncInterfaces.csproj

@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum);netstandard2.1</TargetFrameworks>
-    <!-- Public API not fully documented. -->
-    <NoWarn>$(NoWarn);1591</NoWarn>
     <IsPackable>true</IsPackable>
     <!-- This assembly should never be placed inbox as it is only for downlevel compatibility. -->
     <PackageDescription>Provides the IAsyncEnumerable&lt;T&gt; and IAsyncDisposable interfaces and helper types for .NET Standard 2.0. This package is not required starting with .NET Standard 2.1 and .NET Core 3.0.

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConfiguredAsyncDisposable.cs

@@ -18,6 +18,8 @@ internal ConfiguredAsyncDisposable(IAsyncDisposable source, bool continueOnCaptu
             _continueOnCapturedContext = continueOnCapturedContext;
         }
 
+        /// <summary>Asynchronously releases the unmanaged resources used by the <see cref="T:System.Runtime.CompilerServices.ConfiguredAsyncDisposable" />.</summary>
+        /// <returns>A task that represents the asynchronous dispose operation.</returns>
         public ConfiguredValueTaskAwaitable DisposeAsync() =>
             // as with other "configured" awaitable-related type in CompilerServices, we don't null check to defend against
             // misuse like `default(ConfiguredAsyncDisposable).DisposeAsync()`, which will null ref by design.

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConfiguredCancelableAsyncEnumerable.cs

@@ -36,6 +36,8 @@ public ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait(bool continueOnCapt
         public ConfiguredCancelableAsyncEnumerable<T> WithCancellation(CancellationToken cancellationToken) =>
             new ConfiguredCancelableAsyncEnumerable<T>(_enumerable, _continueOnCapturedContext, cancellationToken);
 
+        /// <summary>Returns an enumerator that iterates asynchronously through collections that enables cancelable iteration and configured awaits.</summary>
+        /// <returns>An enumerator for the <see cref="T:System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable`1" /> class.</returns>
         public Enumerator GetAsyncEnumerator() =>
             // as with other "configured" awaitable-related type in CompilerServices, we don't null check to defend against
             // misuse like `default(ConfiguredCancelableAsyncEnumerable<T>).GetAsyncEnumerator()`, which will null ref by design.

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/EnumeratorCancellationAttribute.cs

@@ -3,9 +3,11 @@
 
 namespace System.Runtime.CompilerServices
 {
+    /// <summary>Allows users of async-enumerable methods to mark the parameter that should receive the cancellation token value from <see cref="M:System.Collections.Generic.IAsyncEnumerable`1.GetAsyncEnumerator(System.Threading.CancellationToken)" />.</summary>
     [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
     public sealed class EnumeratorCancellationAttribute : Attribute
     {
+        /// <summary>Initializes a new instance of the <see cref="T:System.Runtime.CompilerServices.EnumeratorCancellationAttribute" /> class.</summary>
         public EnumeratorCancellationAttribute()
         {
         }