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Issue Description:

When the swift-corelibs-foundation version of URLSession encounters a redirect, it does not call the appropriate delegate method:

urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void)

This only occurs when using a completionHandler-based task. If the task is created without a completionHandler, the delegate method is called.
On Darwin platforms, however, the delegate method is called in both cases.

Steps to reproduce:

I've included a simple Node.js HTTP server to demonstrate the issue.

Use URLSession to request a URL:
http://localhost:8989/first

The server will redirect from /first to /second.

Expected result:

The `willPerformHTTPRedirection` delegate method is called when URLSession performs a completionHandler-based task that results in a redirect.

Actual result:

Darwin:
The delegate method is called.

Linux:
The delegate method is not called.