Consider adding Send extension with ReadOnlySpan<byte> to UdpClient

[paulomorgado]

Consider adding these:

• Send(ReadOnlySpan<Byte>)
• Send(ReadOnlySpan<Byte>, IPEndPoint)

Possible implementation:

#if !NET6_0_OR_GREATER
    extension(global::System.Net.Sockets.UdpClient udpClient)
    {
        public int Send(ReadOnlySpan<byte> datagram, global::System.Net.IPEndPoint? endPoint)
        {
            var rented = ArrayPool<byte>.Shared.Rent(datagram.Length);
            try
            {
                datagram.CopyTo(rented);
                return udpClient.Send(rented, datagram.Length, endPoint);
            }
            finally
            {
                ArrayPool<byte>.Shared.Return(rented);
            }
        }
    }
#endif