Add ResolvePath tests (#276)

Add required computestorage APIs to allow for running tests of
`ResolvePath`.

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

internal/computestorage/computestorage.go

@@ -0,0 +1,48 @@
+//go:build windows
+
+package computestorage
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/windows"
+
+	"github.com/Microsoft/go-winio/internal/interop"
+)
+
+//go:generate go run github.com/Microsoft/go-winio/tools/mkwinsyscall -output zsyscall_windows.go computestorage.go
+
+// https://learn.microsoft.com/en-us/virtualization/api/hcs/reference/hcsformatwritablelayervhd
+//
+//sys hcsFormatWritableLayerVhd(handle windows.Handle) (hr error) = computestorage.HcsFormatWritableLayerVhd?
+
+// FormatWritableLayerVHD formats a virtual disk for use as a writable container layer.
+//
+// If the VHD is not mounted it will be temporarily mounted.
+//
+// NOTE: This API had a breaking change in the operating system after Windows Server 2019.
+// On ws2019 the API expects to get passed a file handle from CreateFile for the vhd that
+// the caller wants to format. On > ws2019, its expected that the caller passes a vhd handle
+// that can be obtained from the virtdisk APIs.
+func FormatWritableLayerVHD(vhdHandle windows.Handle) (err error) {
+	err = hcsFormatWritableLayerVhd(vhdHandle)
+	if err != nil {
+		return fmt.Errorf("failed to format writable layer vhd: %w", err)
+	}
+	return nil
+}
+
+// https://learn.microsoft.com/en-us/virtualization/api/hcs/reference/hcsgetlayervhdmountpath
+//
+//sys hcsGetLayerVhdMountPath(vhdHandle windows.Handle, mountPath **uint16) (hr error) = computestorage.HcsGetLayerVhdMountPath?
+
+// GetLayerVHDMountPath returns the volume path for a virtual disk of a writable container layer.
+func GetLayerVHDMountPath(vhdHandle windows.Handle) (path string, err error) {
+	var mountPath *uint16
+	err = hcsGetLayerVhdMountPath(vhdHandle, &mountPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to get vhd mount path: %w", err)
+	}
+	path = interop.ConvertAndFreeCoTaskMemString(mountPath)
+	return path, nil
+}