Couple more undoc APIs from .NET 9 (#10445)

* Fix File.AppendAllBytesAsync returns

* Default construcvtor summary for DebuggerDisableUserUnhandledExceptionsAttribute

Author: carlossanlop

xml/System.Diagnostics/DebuggerDisableUserUnhandledExceptionsAttribute.xml

@@ -68,7 +68,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes a new instance of the <see cref="T:System.Diagnostics.DebuggerDisableUserUnhandledExceptionsAttribute"/> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.IO/File.xml

@@ -345,8 +345,8 @@
           <para>Asynchronously appends the specified byte array to the end of the file at the given path.</para>
           <para>If the file doesn't exist, this method creates a new file. If the operation is canceled, the task will return in a canceled state.</para>
         </summary>
-        <returns>To be added.</returns>
-        <remarks>A task that represents the asynchronous append operation.</remarks>
+        <returns>A task that represents the asynchronous append operation.</returns>
+        <remarks>To be added.</remarks>
         <exception cref="T:System.ArgumentNullException">
           <paramref name="path" /> is <see langword="null" />.</exception>
         <exception cref="T:System.ArgumentException">