WinHttpHandler - update documentation (#4323)

* WinHttpHandler doc

* Apply suggestions from code review

Co-authored-by: Karel Zikmund <[email protected]>

Co-authored-by: Jan Jahoda <[email protected]>
Co-authored-by: Karel Zikmund <[email protected]>

Author: 3 people

xml/System.Net.Http/WinHttpHandler.xml

@@ -392,8 +392,8 @@
         <Parameter Name="disposing" Type="System.Boolean" />
       </Parameters>
       <Docs>
-        <param name="disposing">To be added.</param>
-        <summary>To be added.</summary>
+        <param name="disposing"><see langword="true" /> to release both managed and unmanaged resources; <see langword="false" /> to release only unmanaged resources.</param>
+        <summary>Releases the unmanaged resources used by the <see cref="T:System.Net.Http.WinHttpHandler" />, and optionally disposes of the managed resources.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -601,8 +601,8 @@
         <ReturnType>System.Collections.Generic.IDictionary&lt;System.String,System.Object&gt;</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets a writable dictionary (that is, a map) of custom properties for the <see cref="T:System.Net.Http.HttpClient" /> requests. The dictionary is initialized empty; you can insert and query key-value pairs for your custom handlers and special processing.</summary>
+        <value>A writable dictionary of custom properties.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>