Add true synchronous GetResponse() method to WebServiceRequestBase

[NateMerritt]

This commit removed WebServiceRequestBase.GetResponse(), which at the time was a sync-over-async antipattern:

		public TResponse GetResponse(CancellationToken cancellationToken = default(CancellationToken))
		{
			// wait for async, which supports timeout
			return GetResponseAsync(cancellationToken).GetAwaiter().GetResult();
		}

The conversation on that commit shows that if a synchronous GetReponse() method is needed then a true synchronous GetResponse() that does synchronous I/O (instead of blocking on an asynchronous call) is preferred. I'm currently writing an API client in which I would like to support synchronous web calls for legacy UI projects. If we port our former Libronix.Utility solution using HttpWebRequest here just for the synchronous GetResponse() then I can use this library, otherwise I'll have to use Libronix.Utility. HttpWebRequest has netstandard2.0 support.