Consider removing Socket.SendFile 2GB limitation on Windows

[stephentoub]

Separated out of #41906

On Windows, the Socket.{Begin}SendFile API inherits the limitation of the Win32 TransmitFile function that constraints it to only being able to send int.MaxValue bytes; anything larger results in an error. This is not a regression, but we should consider supporting this by manually partitioning as the TransmitFile docs suggest. This already works on Linux and macOS.

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