Derive DPG ResponseClassifiers from CoreResponseClassifier

[annelo-msft]

Problem

The DPG implementation of per-operation response classifiers currently derives from the ResponseClassifier type. But, the base ResponseClassifier cannot be directly modified in a way that allows us to efficiently compose a chain of ResponseClassificationHandlers with a ResponseClassifier at the end of the chain.

In PR 26547, we introduced a new CoreResponseClassifier type that allows us to both add status code classifiers and evaluate responses against them efficiently.

What we'll do

We'll replace the old DPG per-operation ResponseClassifier implementation with the new one (below) deriving from CoreResponseClassifier.

Old DPG Per-Operation ResponseClassifier

private sealed class ResponseClassifier200404 : ResponseClassifier
{
    private static ResponseClassifier _instance;
    public static ResponseClassifier Instance => _instance ??= new ResponseClassifier200404();
    public override bool IsErrorResponse(HttpMessage message)
    {
        return message.Response.Status switch
        {
            200 => false,
            404 => false,
            _ => true
        };
    }
}

New DPG Per-Operation ResponseClassifier

private sealed class ResponseClassifier200404 : CoreResponseClassifier
{
    private static CoreResponseClassifier _instance;
    public static CoreResponseClassifier Instance => _instance ??= new ResponseClassifier200404();

    public ResponseClassifier200404() : base(stackalloc int[]{ 200, 404 })
    {
    }
}

[annelo-msft]

In addition, we'll want to create the HttpMessage as follows:

var message = _pipeline.CreateMessage(context, ResponseClassifier200404.Instance); // passing the appropriate classifier

This should work for classifiers that don't derive from CoreResponseClassifier as well (like the one for the head request test case). They are just much more efficient when they derive from CoreResponseClassifier, so we want to use it as much as possible.

[AlexanderSher]

private static ResponseClassifier _responseClassifier200404;
private static ResponseClassifier ResponseClassifier200404 => _responseClassifier200404 ??= new CoreResponseClassifier(stackalloc int[]{ 200, 404 });

Usage:

var message = _pipeline.CreateMessage(context, ResponseClassifier200404); 

[AlexanderSher]

    private sealed class ResponseClassifierOverride200To300400To500 : ResponseClassifier
    {
        public override bool IsErrorResponse(HttpMessage message)
        {
            return message.Response.Status switch
            {
                >= 200 and < 300 => false,
                >= 400 and < 500 => false,
                _ => true
            };
        }
    }
    
    private static ResponseClassifier _responseClassifier200To300400To500;
    private static ResponseClassifier ResponseClassifier200To300400To500 => _responseClassifier200To300400To500 ??= new ResponseClassifierOverride200To300400To500();