Support HTTP response streaming in legacy .NET runtimes

Currently in .NET 4.x HTTP responses are never streamed. Instead, the deserialized objects are streamed after the full HTTP response body is read into a buffer by the HttpClient. This results in a higher time-to-first-result in .NET 4.

This limitation is in place because:

• Different behaviors around HttpClient.Dispose in .NET 4 may cause IOExceptions (see NCBC-3433)
• HttpResponseMessage doesn't have a finalizer in .NET 4 so failure to dispose of the returned IQueryResult<T> (or similar) could cause HTTP connection leaks. When combined with the default limit of 2 connections per HTTP server in .NET 4 this could easily lead to outages.

We should address our Dispose patterns to avoid the first problem and then provide a way for users to opt-in to HTTP streaming in .NET 4 if they are aware of the second problem and properly dispose of returned IQueryResult<T>, IViewResult<T>, and IAnalyticsResult<T> objects.

https://www.couchbase.com/forums/t/streaming-result-of-queries/37043/8