Switch from sycall to windows (#295)

Where ever possible, use `golang.org/x/sys/windows` instead of `syscall`
(which has been deprecated since go1.11).

Using `windows.LocalFree` requires using `unsafe.Pointer`, which ensures
that the Go garbage collector does not try to free memory pre-maturely
if it was previously declared as a pointer.

Since `syscall.Handle` is part of API for `vhd` package, it was left
unchanged.

For security descriptor functions, switch to using
`windows.SECURITY_DESCRIPTOR` to avoid unnecessary byte manipulation and
panics due to missing input validation and error checking.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

pkg/etw/eventdata.go

@@ -6,7 +6,8 @@ package etw
 import (
 	"bytes"
 	"encoding/binary"
-	"syscall"
+
+	"golang.org/x/sys/windows"
 )
 
 // eventData maintains a buffer which builds up the data for an ETW event. It
@@ -69,6 +70,6 @@ func (ed *eventData) writeUint64(value uint64) {
 }
 
 // writeFiletime appends a FILETIME to the buffer.
-func (ed *eventData) writeFiletime(value syscall.Filetime) {
+func (ed *eventData) writeFiletime(value windows.Filetime) {
 	_ = binary.Write(&ed.buffer, binary.LittleEndian, value)
 }