[C#] C# stub classes should use description attributes from XML file

[rca22]

The description fields for messages should result in C# comments in the generated code.

e.g.
<sbe:message name="MyMessage" id="201" semanticType="V" description="This is my message type."> <field name="MarketDepth" id="264" type="uint8" description="0=Full Book, 1=Top of Book, n=Number of Levels."/> ...

should result in

/// <summary>
/// This is my message type
/// </summary>
public sealed partial class MyMessage
{
...
        /// <summary>
        /// 0=Full Book, 1=Top of Book, n=Number of Levels.
        /// </summary>
        public byte MarketDepth
        {
        ...
        }
}

This will aid in understanding the C# classes without having to refer back to the XML frequently.

[mjpt777]

We would welcome a PR for this or accept sponsorship for the development.