windows: replace all StringToUTF16 calls with UTF16FromString

`StringToUTF16` is deprecated and will panic if given an "invalid"
string (in particular, one that has a null byte in it).  The replacement
function is `UTF16FromString`, and it returns an error if there was
a problem.

This change replaces all uses of `StringToUTF16` with `UTF16FromString`.
The `service` struct now no longer stores a `string` name but rather
a `*uint16` pointer to the name.

It should not be possible to panic due to UTF16 string conversion
at this point.

Fixes golang/go#73006

Change-Id: Idce9cdbb4651fef8481f0cad19b5df0314fd4277
Reviewed-on: https://go-review.googlesource.com/c/sys/+/659936
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

windows/registry/key.go

@@ -164,7 +164,12 @@ loopItems:
 func CreateKey(k Key, path string, access uint32) (newk Key, openedExisting bool, err error) {
 	var h syscall.Handle
 	var d uint32
-	err = regCreateKeyEx(syscall.Handle(k), syscall.StringToUTF16Ptr(path),
+	var pathPointer *uint16
+	pathPointer, err = syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return 0, false, err
+	}
+	err = regCreateKeyEx(syscall.Handle(k), pathPointer,
 		0, nil, _REG_OPTION_NON_VOLATILE, access, nil, &h, &d)
 	if err != nil {
 		return 0, false, err
@@ -174,7 +179,11 @@ func CreateKey(k Key, path string, access uint32) (newk Key, openedExisting bool
 
 // DeleteKey deletes the subkey path of key k and its values.
 func DeleteKey(k Key, path string) error {
-	return regDeleteKey(syscall.Handle(k), syscall.StringToUTF16Ptr(path))
+	pathPointer, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return err
+	}
+	return regDeleteKey(syscall.Handle(k), pathPointer)
 }
 
 // A KeyInfo describes the statistics of a key. It is returned by Stat.

windows/registry/value.go

@@ -340,7 +340,11 @@ func (k Key) SetBinaryValue(name string, value []byte) error {
 
 // DeleteValue removes a named value from the key k.
 func (k Key) DeleteValue(name string) error {
-	return regDeleteValue(syscall.Handle(k), syscall.StringToUTF16Ptr(name))
+	namePointer, err := syscall.UTF16PtrFromString(name)
+	if err != nil {
+		return err
+	}
+	return regDeleteValue(syscall.Handle(k), namePointer)
 }
 
 // ReadValueNames returns the value names of key k.