Add CreateContentReadStreamAsync documentation to various Content classes (#4747)

* Add CreateContentReadStreamAsync documentation to various Content classes

* Update xml/System.Net.Http/HttpContent.xml

Co-authored-by: Carlos Sanchez <[email protected]>

Co-authored-by: Jan Jahoda <[email protected]>
Co-authored-by: Carlos Sanchez <[email protected]>

Author: 3 people

xml/System.Net.Http/HttpContent.xml

@@ -365,10 +365,21 @@
         <Parameter Name="cancellationToken" Type="System.Threading.CancellationToken" Index="0" FrameworkAlternate="net-5.0" />
       </Parameters>
       <Docs>
-        <param name="cancellationToken">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="cancellationToken">The cancellation token to cancel the operation.</param>
+        <summary>Serializes the HTTP content to a memory stream as an asynchronous operation.</summary>
+        <returns>The task object representing the asynchronous operation.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ This operation will not block. The returned <xref:System.Threading.Tasks.Task%601> object will complete after all of the content has been written to the memory stream.  
+  
+ Once the operation completes, the  <xref:System.Threading.Tasks.Task%601.Result%2A> property on the returned task object contains the memory stream that represents the HTTP content. The returned stream can then be used to read the content using various stream APIs.  
+  
+ The <xref:System.Net.Http.HttpContent.CreateContentReadStreamAsync%2A> method buffers the content to a memory stream. Derived classes can override this behavior if there is a better way to retrieve the content as stream. For example, a byte array or a string could use a more efficient method way such as wrapping a read-only <xref:System.IO.MemoryStream> around the bytes or string.)  
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <MemberGroup MemberName="Dispose">

xml/System.Net.Http/MultipartContent.xml

@@ -279,10 +279,21 @@
         <Parameter Name="cancellationToken" Type="System.Threading.CancellationToken" Index="0" FrameworkAlternate="net-5.0" />
       </Parameters>
       <Docs>
-        <param name="cancellationToken">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="cancellationToken">The cancellation token to cancel the operation.</param>
+        <summary>Serializes the HTTP content to a stream using the multipart/* encoding as an asynchronous operation.</summary>
+        <returns>The task object representing the asynchronous operation.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+ This method overrides <xref:System.Net.Http.HttpContent.CreateContentReadStreamAsync%2A?displayProperty=nameWithType> to use a custom stream that contains an array, with each HTTP content and its boundary encoded and serialized to a <xref:System.IO.MemoryStream> instance.
+
+ This operation will not block. The returned <xref:System.Threading.Tasks.Task%601> object will complete after all of the content has been written to the memory stream.  
+  
+ Once the operation completes, the <xref:System.Threading.Tasks.Task%601.Result%2A?displayProperty=nameWithType> property on the returned task object contains the stream that represents the multipart/* encoded HTTP content. The returned stream can then be used to read the content using various stream APIs.  
+  
+ ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="Dispose">