Corrected `HvsockConn` `CloseRead`/`Write` to check if the socket
has been closed before attempting to shutdown the socket for
reading or writing.
Additionally, `shutdown` was not respecting whether to shutdown reading
or writing, and only shutting down the socket for reading.
Added `IsClosed` function to `win32File` (and therefore `win32Pipe` and
`win32MessageBytePipe`) and `HvsockConn` to check if the socket/pipe
has been closed already.
Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>
