Windows produces different error codes for empty paths compared to Linux/Darwin

[jmschonfeld]

Brought up at swiftlang/swift-corelibs-foundation#5074 (comment)

Linux/Darwin provide various error codes like .fileReadNoSuchFile when provided with an empty path. However on Windows we currently throw .fileReadInvalidFileName errors. We should make these behaviors consistent. Originally SCL-F already threw .fileReadInvalidFileName but Darwin threw .fileReadNoSuchFile. With the swift rewrite of FileManager we updated Linux to match what Darwin does, but Windows has still diverged. We should update Windows to match the Linux/Darwin behavior so that we have consistency across our platforms