Consolidate Rest Client service method generation

[AlexanderSher]

Consolidate generation of Rest Client (for DPG - public client is treated as Rest Client) service methods with ability to switch between HLC-style method structure, e.g.:

CreateXxxRequest(BinaryData bd)
{
    var rc = new RequestContent();
    rc.Writer.Write(bd.ToArray());
    request.RequestContent = rc;
}

Response<Y> Xxx(BinaryData bd)
{
    ///
    var message = CreateXxxRequest(bd);
    ///
}

to DPG-style method structure

Response<Y> XxxValue(BinaryData bd)
{
    var rc = new RequestContent();
    rc.Writer.Write(bd.ToArray());
    var response = Xxx(rc);
    return (Y)response;
}

Response Xxx(RequestContent rc)
{
    var message = CreateXxxRequest(rc);
    ///
}

CreateXxxRequest(RequestContent rc)
{
    request.RequestContent = rc;
}

[ArthurMa1978]

Push to MGC plugin