Issue Description:

Using the in URLSession.seekInputStream(to🙂 method in a Linux environment crashes the entire application on the following line:

https://github.com/apple/swift-corelibs-foundation/blob/master/Foundation/URLSession/NativeProtocol.swift#L264

There is an existing PR that implements the method to some degree, but would likely need some cleaning up before merging:

#1629

I think implementing this method is particularly important in a server-side environment where it’s causing a lot of random and difficult-to-debug crashes in Vapor projects.