swift-server
Add testProxyStreamingNoDeadlock test
Because there is a maximum number of concurrent connections per host it is possible for the client to deadlock itself when making requests with a streamed body if the body data is itself requested from the same host.
If we reach the maximum number of concurrent requests for a certain host, and if all active tasks use a streamed body that obtains its data from requests to the same host, then the bodies will never be obtained as the requests they need to make will be put on a queue whose ability to dequeue them depends on their very result -> deadlock.
Just as a heads up, the main development branch has been changed to main, following the Swift policy on this.
This PR has been re-targeted to main and should just work. However when performing rebases etc please keep this in mind -- you may want to fetch the main branch and rebase onto the main branch from now on since master is not up-to-date anymore and is going to be deleted shortly.
