Documentation comment auto completion should not generate <returns> for indexers

[nxtn]

Version Used: Visual Studio 2019 Version 16.3

Steps to Reproduce:

public class Program
{
    public object this[int index]
    {
        get => throw new System.NotImplementedException();
        set => throw new System.NotImplementedException();
    }
}

+Expected Behavior
-Actual Behavior

public class Program
{
    /// <summary>
    /// 
    /// </summary>
    /// <param name="index"></param>
+    /// <value></value>
+    /// -or-
+    /// <param name="index"></param>
-    /// <returns></returns>
    public object this[int index]
    {
        get => throw new System.NotImplementedException();
        set => throw new System.NotImplementedException();
    }
}

[sharwell]

Closely related to #8627